Combined effects of oleic,linoleic and linolenic acids on lactation performance and the milk fatty acid profile in lactating dairy cows

The potential combined effects of oleic, linoleic and linolenic acids supplementation on lactation performance and the milk fatty acid (FA) profile in dairy cows have not been well investigated. Our objective was to examine the effects of supplementation with a combination of these FA as well as the effects of removing each from the combination on lactation performance and the milk FA profile in dairy cows. Eight Holstein cows (101±11 days in milk) received four intravenously infused treatments in a 4×4 Latin square design, and each period lasted for 12 days which consisted of 5 days of infusion and 7 days of recovery. The control treatment (CTL) contained 58.30, 58.17 and 39.96 g/day of C18: 1 cis-9; C18: 2 cis-9, cis-12; and C18: 3 cis-9, cis-12, cis-15, respectively. The other three treatments were designated −−C18: 1 (20.68, 61.17 and 41.72 g/day of C18: 1 cis-9; C18: 2 cis-9, cis-12; and C18: 3 cis-9, cis-12, cis-15, respectively), −C18: 2 (61.49, 19.55 and 42.13 g/day of C18: 1 cis-9; C18: 2 cis-9, cis-12; and C18: 3 cis-9, cis-12, cis-15, respectively) and −C18: 3 (60.89, 60.16 and 1.53 g/day of C18: 1 cis-9; C18: 2 cis-9, cis-12; and C18: 3 cis-9, cis-12, cis-15, respectively). Dry matter intake and lactose content were not affected by the treatments, but the milk protein content was lower in cows treated with −C18: 2 than that in CTL-treated cows. Milk yield as well as milk fat, protein and lactose yields were higher in cows treated with −C18: 3 than the yields in CTL-treated cows, and these yields increased linearly as the unsaturation degree of the supplemental FA decreased. Compared with the CTL treatment, the −C18: 2 treatment decreased milk C18: 2 cis-9 content (by 2.80%) and yield (by 22.12 g/day), and the −C18: 3 treatment decreased milk C18: 3 cis-9, cis-12, cis-15 content (by 2.72%) and yield (by 22.33 g/day). In contrast, removing C18: 1 cis-9 did not affect the milk content or yield of C18: 1 cis-9. The −C18: 2-treated cows had a higher C18: 1 cis-9 content and tended to have a higher C18: 1 cis-9 yield than CTL-treated cows. The yields of C8: 0, C14: 0 and C16: 0 as well as <C16: 0 tended to increase linearly as the unsaturation degree of the supplemental FA decreased (P=0.06, 0.07, 0.07 and 0.09, respectively). These results indicated that supplementation with C18 unsaturated FA might not independently affect the lactation performance and the milk FA profile of dairy cows.     

The influence of grass silage-to-maize silage ratio and concentrate composition on methane emissions,performance and milk composition of dairy cows

It is well-established that altering the proportion of starch and fibre in ruminant diets can alter ruminal and post-ruminal digestion, although quantitative evidence that this reduces enteric methane (CH₄) production in dairy cattle is lacking. The objective of this study was to examine the effect of varying grass-to-maize silage ratio (70 : 30 and 30 : 70 DM basis), offered ad libitum, with either a concentrate that was high in starch or fibre, on CH₄ production, intake, performance and milk composition of dairy cows. A total of 20 cows were allocated to one of the four experimental diets in a two-by-two factorial design run as a Latin square with each period lasting 28 days. Measurements were conducted during the final 7 days of each period. Cows offered the high maize silage ration had a higher dry matter intake (DMI), milk yield, milk energy output and lower CH₄ emissions when expressed per kg DMI and per unit of ingested gross energy, but there was no difference in total CH₄ production. Several of the milk long-chain fatty acids (FA) were affected by forage treatment with the most notable being an increase in 18:0, 18:1 c9, 18:2 c9 c12 and total mono unsaturated FA, observed in cows offered the higher inclusion of maize silage, and an increase in 18:3 c9 c12 c15 when offered the higher grass silage ration. Varying the composition of the concentrate had no effect on DMI or milk production; however, when the high-starch concentrate was fed, milk protein concentration and milk FAs, 10:0, 14:1, 15:0, 16:1, increased and 18:0 decreased. Interactions were observed for milk fat concentration, being lower in cows offered high-grass silage and high-fibre concentrates compared with the high-starch concentrate, and FA 17:0, which was the highest in milk from cows fed the high-grass silage diet supplemented with the high-starch concentrate. In conclusion, increasing the proportion of maize silage in the diets of dairy cows increased intake and performance, and reduced CH₄ production, but only when expressed on a DM or energy intake basis, whereas starch-to-fibre ratio in the concentrate had little effect on performance or CH₄ production.     

Effect of replacing grass silage with maize silage in the diet on bovine milk fatty acid composition

Even though extensive research has examined the role of nutrition on milk fat composition, there is less information on the impact of forages on milk fatty acid (FA) composition. In the current study, the effect of replacing grass silage (GS) with maize silage (MS) as part of a total mixed ration on animal performance and milk FA composition was examined using eight multiparous mid-lactation cows in a replicated 4 × 4 Latin square with 28-day experimental periods. Four treatments comprised the stepwise replacement of GS with MS (0, 160, 334 and 500 g/kg dry matter (DM)) in diets containing a 54 : 46 forage : concentrate ratio on a DM basis. Replacing GS with MS increased (P < 0.001) the DM intake, milk yield and milk protein content. Incremental replacement of GS with MS in the diet enhanced linearly (P < 0.001) the proportions of 6:0-14:0, decreased (P < 0.01) the 16:0 concentrations, but had no effect on the total milk fat saturated fatty acid content. Inclusion of MS altered the distribution of trans-18:1 isomers and enhanced (P < 0.05) total trans monounsaturated fatty acid and total conjugated linoleic acid content. Milk total n-3 polyunsaturated fatty acid (PUFA) content decreased with higher amounts of MS in the diet and n-6 PUFA concentration increased, leading to an elevated n-6 : n-3 PUFA ratio. Despite some beneficial changes associated with the replacement of GS with MS, the overall effects on milk FA composition would not be expected to substantially improve long-term human health. However, the role of forages on milk fat composition must also be balanced against the increases in total milk and protein yield on diets containing higher proportions of MS.     

Effects of dehydrated lucerne and soya bean meal on milk production and composition,nutrient digestion,and methane and nitrogen losses in dairy cows receiving two different forages

Dehydrated lucerne is used as a protein source in dairy cow rations, but little is known about the effects of lucerne on greenhouse gas production by animals. Eight Holstein dairy cows (average weight: 582 kg) were used in a replicated 4×4 Latin square design. They received diets based on either maize silage (M) or grass silage (G) (45% of diet on dry matter (DM) basis), with either soya bean meal (15% of diet DM) completed with beet pulp (15% of diet DM) (SP) or dehydrated lucerne (L) (30% of diet DM) as protein sources; MSP, ML, GSP and GL diets were calculated to meet energy requirements for milk production by dairy cows and degradable protein for rumen microbes. Dry matter intake (DMI) did not differ among diets (18.0 kg/day DMI); milk production was higher with SP diets than with L diets (26.0 v. 24.1 kg/day), but milk production did not vary with forage type. Milk fatty-acid (FA) composition was modified by both forage and protein sources: L and G diets resulted in less saturated FA, less linoleic acid, more trans-monounsaturated FA, and more linolenic acid than SP and M diets, respectively. Enteric methane (CH₄) production, measured by the SF₆ tracer method, was higher for G diets than for M diets, but did not differ with protein source. The same effects were observed when CH₄ was expressed per kg milk. Minor effects of diets on rumen fermentation pattern were observed. Manure CH₄ emissions estimated from faecal organic matter were negatively related to diet digestibility and were thus higher for L than SP diets, and higher for M than G diets; the resulting difference in total CH₄ production was small. Owing to diet formulation constraints, N intake was higher for SP than for L diets; interaction between forage type and protein source was significant for N intake. The same statistical effects were found for N in milk. Faecal and urinary N losses were determined from total faeces and urine collection. Faecal N output was lower for M than for G diets but did not differ between protein sources. Urinary N output did not differ between forage types, but was lower for cows fed L diets than for cows fed SP diets, potentially resulting in lower ammonia emissions with L diets. Replacing soya bean meal plus beet pulp with dehydrated lucerne did not change CH₄ production, but resulted in more N in faeces and less N in urine.     

The effect of varying proportion and chop length of lucerne silage in a maize silage-based total mixed ration on diet digestibility and milk yield in dairy cattle

The objective was to assess the effects of inclusion rate and chop length of lucerne silage, when fed in a total mixed ration (TMR), on milk yield, dry matter (DM) intake (DMI) and digestion in dairy cows. Diets were formulated to contain a 50 : 50 ratio of forage : concentrate (DM basis) and to be isonitrogenous (170 g/kg CP). The forage portion of the offered diets was comprised of maize and lucerne silage in proportions (DM basis) of either 25 : 75 (high Lucerne (HL)) or 75 : 25 (low lucerne (LL)). Lucerne was harvested and conserved as silage at either a long (L) or short (S) chop length. These variables were combined in a 2×2 factorial arrangement to give four treatments (HLL, HLS, LLL, LLS) which were fed in a Latin square design study to Holstein dairy cows in two separate experiments. In total, 16 and 8 multiparous, mid-lactation cows were used in experiments 1 and 2, respectively. To ensure sufficient silage for both experiments, different cuts of lucerne silage (taken from the same sward) were used for each experiment: first cut for experiment 1 (which was of poorer quality) and second cut for experiment 2. Dry matter intake, milk yield and milk composition where measured in both experiments, and total tract digestibility and nitrogen (N) balance were assessed using four cows in experiment 2. In experiment 1, cows fed LL had increased DMI (+3.2 kg/day), compared with those fed HL. In contrast, there was no difference in DMI due to lucerne silage inclusion rate in experiment 2. A reduction in milk yield was observed with the HL treatment in both experiment 1 and 2 (−3.0 and −2.9 kg/day, respectively). The HL diet had reduced digestibility of DM and organic matter (OM) (−3% and −4%, respectively), and also reduced the efficiency of intake N conversion into milk N (−4%). The S chop length increased total tract digestibility of DM and OM (both +4%), regardless of inclusion rate. Inclusion of lucerne silage at 25% of forage DM increased milk yield relative to 75% inclusion, but a S chop length partially mitigated adverse effects of HL on DMI and milk yield in experiment 1 and on DM digestibility in experiment 2.     

The effect of N-fertilisation rate or inclusion of red clover to timothy leys on fatty acid composition in milk of dairy cows fed a commercial silage : concentrate ratio

The aim of this experiment was to, under typical Swedish production conditions, evaluate the effects of grass silages subjected to different N-fertilisation regimes fed to dairy cows on the fatty acid (FA) composition of their milk, and to compare the grass silages in this respect to red clover-dominated silage. Grass silages made from first year Phleum pratense L. leys subjected to three N-fertilisation regimes (30, 90 and 120 kg N/ha, designated G-30, G-90 and G-120, respectively) and a mixed red clover–grass silage (Trifolium pratense L. and P. pratense L.; 60/40 on dry matter (DM) basis, designated RC–G) were produced. The experiment was conducted as a change-over design, including 24 primiparous and multiparous dairy cows of the Swedish Red breed, each of which was allocated to three of the four diets. The cows were offered 11 kg DM of silage and 7 kg concentrates. The silages had similar DM and energy concentrations. The CP concentration increased with increase in N-fertilisation level. There was a linear increase in DM intake of the different silages with increased N fertilisation. There were also differences in concentrations of both individual and total FAs amongst silages. The daily milk production (kg/day) did not significantly differ between treatments, but G-30 silage resulted in higher concentrations of 18:2n-6 in the milk compared with the other two grass silages. The highest concentrations of 18:3n-3 and cis-9, trans-11 18:2 were found in milk from cows offered the RC–G silage. The G-30 diet resulted in higher concentration of 18:2n-6 and the same concentration of 18:3n-3 in the milk as the other grass silages, despite lower intake levels of these FAs. The apparent recoveries of 18:3n-3 from feed to milk were 5.74%, 4.27%, 4.10% and 5.31% for G-30, G-90, G-120 and RC–G, respectively. A higher recovery when red clover is included in the diet confirms previous reports. The higher apparent recovery of 18:3n-3 on the G-30 treatment may be related to the lower silage DM intake, which led to a higher relative proportion of ingested FAs originating from concentrates compared with the G-90 and G-120 diets. With the rates and types of concentrates used in this study, the achieved differences in FA composition among the silages were not enough to influence the concentrations of unsaturated FAs in milk.     

Effect of rate of substitution of processed, urea-treated whole-crop wheat for grass silage on the intake, milk production and diet digestibility in dairy cows and ruminal metabolism in vitro

The effect of rate of substitution of processed, urea-treated whole-crop wheat (pWCW) for grass silage on intake, performance and whole-tract digestibility was evaluated using 44 dairy cows. Cows received 10.5 kg of concentrates per day and one of the following forage mixtures (dry matter (DM) basis): grass silage alone (W-0); 0.75 grass silage, 0.25 pWCW (W-25); 0.5 grass silage, 0.5 pWCW (W-50) or 0.25 grass silage, 0.75 pWCW (W-75). Forage DM intake increased linearly with inclusion rate of pWCW from 9.7 kg DM per day in cows fed W-0 to 14.6 kg DM per day in W-75. By contrast, milk and protein yield (kg/day) were higher (P < 0.05) in cows receiving W-25 compared with W-0, but there was no effect (P>0.05) of treatment on fat yield (kg/day). From week 11 of the experiment onwards, body condition score increased with rate of inclusion of pWCW (P < 0.05). Whole-tract apparent digestibility of organic matter (OM) and fibre (kg/kg), decreased linearly with rate of inclusion of pWCW. Assuming a constant digestibility of starch in the other diet components, the apparent digestibility of starch in pWCW was 0.95 kg/kg and was not affected by rate of inclusion (P>0.05). Four continuous culture vessels were used to determine the effect of rate of inclusion of pWCW on ruminal metabolism in four periods, each of 14 d duration with sampling conducted on days 9 to 14. Vessel ammonia concentration increased linearly (P < 0.05) with rate of inclusion of pWCW whilst mean pH tended (P = 0.06) to decrease. The ratio of acetate to propionate increased from 2.5 in vessels receiving W-0 to 3.2 in those receiving W-75 (P < 0.001). There was no effect (P>0.05) of treatment on digestibility (g/g) of OM, fibre or starch or microbial protein flow (g/day). It is concluded that forage DM intake increased linearly with rate of inclusion of pWCW, but there was no further improvement in milk yield from inclusion rates above 0.25 of the forage DM, with body condition score increasing instead. Increasing the inclusion rate of pWCW resulted in a more ketogenic volatile fatty acid profile but did not affect the efficiency of microbial protein synthesis when determined in vitro.     

Relationships between methane emission of Holstein Friesian dairy cows and fatty acids,volatile metabolites and non-volatile metabolites in milk

This study investigated the relationships between methane (CH₄) emission and fatty acids, volatile metabolites (V) and non-volatile metabolites (NV) in milk of dairy cows. Data from an experiment with 32 multiparous dairy cows and four diets were used. All diets had a roughage : concentrate ratio of 80 : 20 based on dry matter (DM). Roughage consisted of either 1000 g/kg DM grass silage (GS), 1000 g/kg DM maize silage (MS), or a mixture of both silages (667 g/kg DM GS and 333 g/kg DM MS; 333 g/kg DM GS and 677 g/kg DM MS). Methane emission was measured in climate respiration chambers and expressed as production (g/day), yield (g/kg dry matter intake; DMI) and intensity (g/kg fat- and protein-corrected milk; FPCM). Milk was sampled during the same days and analysed for fatty acids by gas chromatography, for V by gas chromatography–mass spectrometry, and for NV by nuclear magnetic resonance. Several models were obtained using a stepwise selection of (1) milk fatty acids (MFA), V or NV alone, and (2) the combination of MFA, V and NV, based on the minimum Akaike’s information criterion statistic. Dry matter intake was 16.8±1.23 kg/day, FPCM yield was 25.0±3.14 kg/day, CH₄ production was 406±37.0 g/day, CH₄ yield was 24.1±1.87 g/kg DMI and CH₄ intensity was 16.4±1.91 g/kg FPCM. The observed CH₄ emissions were compared with the CH₄ emissions predicted by the obtained models, based on concordance correlation coefficient (CCC) analysis. The best models with MFA alone predicted CH₄ production, yield and intensity with a CCC of 0.80, 0.71 and 0.69, respectively. The best models combining the three types of metabolites included MFA and NV for CH₄ production and CH₄ yield, whereas for CH₄ intensity MFA, NV and V were all included. These models predicted CH₄ production, yield and intensity better with a higher CCC of 0.92, 0.78 and 0.93, respectively, and with increased accuracy (C_b) and precision (r). The results indicate that MFA alone have moderate to good potential to estimate CH₄ emission, and furthermore that including V (CH₄ intensity only) and NV increases the CH₄ emission prediction potential. This holds particularly for the prediction model for CH₄ intensity.     

High- and low-purity glycerine supplementation to dairy cows in early lactation: effects on silage intake,milk production and metabolism

This study evaluated the effects of supplemental low- and high-purity glycerine on silage intake, milk yield and composition, plasma metabolites and body condition score (BCS) in dairy cows. A total of 42 cows of the Swedish Red Breed, housed in individual tie stalls, were fed 0.25 kg of low- or high-purity glycerine on top of concentrate, twice daily, during the first 4 weeks of lactation. One-third of the cows acted as controls, receiving no glycerine. Silage was fed for ad libitum intake and concentrate was fed at restricted level of intake, about 6 kg/day for primiparous cows and 7 kg/day for multiparous cows. Feed refusals were weighed daily. Cows were milked twice daily, milk yield was recorded on four occasions per week and milk samples were collected simultaneously. Blood samples were drawn from the coccygeal vessel once a week. Low- and high-purity glycerine had no effect on silage or total dry matter intake (P = 0.38 and P = 0.75, respectively) or on BCS (P = 0.45). Cows fed high-purity glycerine tended to have higher milk yield than control cows (P = 0.06). Milk composition tended to differ among treatments. No main effects of treatment on concentration of glycerine (P = 0.44), glucose (P = 0.78), insulin (P = 0.33), non-esterified fatty acids (P = 0.33) and β-hydroxybutyrate (P = 0.15) in plasma. These data indicate that high-purity glycerine has the potential to increase milk yield, as well as enhance the milk protein concentration and milk fat + protein yield.     

Effect of palmitic acid on the mitigation of milk fat depression syndrome caused by trans-10, cis-12-conjugated linoleic acid in grazing dairy cows

The objective of the study was to evaluate the effect of adding protected palmitic acid (PA) to the ration of grazing dairy cows supplemented with protected conjugated linoleic acid (CLA) on milk production, chemical composition and fat profile. Six cows were used, 3/4 American Swiss × Zebu, under a rotational grazing system in a mixed sward with Cynodon plectostachyus, Brachiaria decumbens and Brachiaria brizantha. Furthermore, each cow received daily 4 kg concentrates and 8 kg sorghum silage, which made up the basal diet. The cows were distributed into three two-cow groups. Three treatments were randomly assigned to the groups, using a cross design: (1) control (basal diet), (2) basal diet + CLA (50 g/d) and (3) basal diet + CLA (50 g/d) + PA (412 g/d). The following variables were evaluated: forage intake, milk production, protein, fat and lactose concentration in milk, and milk fatty acid (FA) profile. There were no differences in forage intake between treatments; however, there were differences in milk production, protein, fat and lactose yield and fat concentration, which increased significantly in group CLA + PA when compared with group CLA. The concentration of FA synthesised de novo was lower when PA was included in the diet. Adding PA to the diet of grazing cows mitigates the milk fat decline caused by including trans-10, cis-12 CLA in the diet.     

Grass silage particle size when fed with or without maize silage alters performance,reticular pH and metabolism of Holstein-Friesian dairy cows

The particle size of the forage has been proposed as a key factor to ensure a healthy rumen function and maintain dairy cow performance, but little work has been conducted on ryegrass silage (GS). To determine the effect of chop length of GS and GS:maize silage (MS) ratio on the performance, reticular pH, metabolism and eating behaviour of dairy cows, 16 multiparous Holstein-Friesian cows were used in a 4×4 Latin square design with four periods each of 28-days duration. Ryegrass was harvested and ensiled at two mean chop lengths (short and long) and included at two ratios of GS:MS (100:0 or 40:60 dry matter (DM) basis). The forages were fed in mixed rations to produce four isonitrogenous and isoenergetic diets: long chop GS, short chop GS, long chop GS and MS and short chop GS and MS. The DM intake (DMI) was 3.2 kg/day higher (P<0.001) when cows were fed the MS than the GS-based diets. The short chop length GS also resulted in a 0.9 kg/day DM higher (P<0.05) DMI compared with the long chop length. When fed the GS:MS-based diets, cows produced 2.4 kg/day more (P<0.001) milk than when fed diets containing GS only. There was an interaction (P<0.05) between chop length and forage ratio for milk yield, with a short chop length GS increasing yield in cows fed GS but not MS-based diets. An interaction for DM and organic matter digestibility was also observed (P<0.05), where a short chop length GS increased digestibility in cows when fed the GS-based diets but had little effect when fed the MS-based diet. When fed the MS-based diets, cows spent longer at reticular pH levels below pH 6.2 and pH 6.5 (P<0.01), but chop length had little effect. Cows when fed the MS-based diets had a higher (P<0.05) milk fat concentration of C18 : 2n-6 and total polyunsaturated fatty acids compared with when fed the GS only diets. In conclusion, GS chop length had little effect on reticular pH, but a longer chop length reduced DMI and milk yield but had little effect on milk fat yield. Including MS reduced reticular pH, but increased DMI and milk performance irrespective of the GS chop length.     

Milk fatty acid profile of Peruvian Criollo and Brown Swiss cows in response to different diet qualities fed at low and high altitude

Two identical experimental protocols were followed at 200 and 3,600 m above sea level (a.s.l.) determining the changes of the milk fatty acid (FA) profile of Brown Swiss (BS) and indigenous Peruvian Criollo cows (CR) as a response to diets which were designed to cover the variation in feed quality caused by season. At each site (altitude), six BS and six CR cows, adapted to >3,500 m a.s.l., were fed three dietary treatments (DS, dry-season forage; RS rainy-season forage; OC, diet optimised to meet the cow's requirements) in a 2 × 2 × 3-factorial arrangement. Intakes of FA and milk yield increased from diet DS (low quality diet) to RS and OC (high quality diet) for both cow types. Milk fat proportions of conjugated linoleic acid (CLA), C18:3 c9,c12,c15, total n-3 and polyunsaturated FA (PUFA) were highest (p < 0.05) with diet OC and higher in the lowlands than in the highlands. Low intakes of diet DS obviously resulted in a ruminal energy deficiency and body lipid mobilisation. The ruminal energy deficiency with diet DS was especially pronounced in BS, apparently reducing biohydrogenation rate and leading to lower proportions of C18:0 and higher proportions of C18:3 c9,c12,c15 in milk fat (p < 0.05). Especially C18:3 c9,c12,c15 intake did not concur with its proportion in milk fat, suggesting a strong dependence on energy status. Milk yield and FA excretion with milk were higher for BS than for CR (p < 0.05) with all three diets although milk fat content was lower (p < 0.05) for BS than CR. Milk fat of BS was richer in CLA and PUFA than milk fat of CR (p < 0.05). The desaturase indices for 18 FA were also higher for BS than CR (p < 0.05), suggesting a slightly higher Δ9-desaturase activity for BS, especially with diet DS. Milk fat content was generally higher at the high altitude than at the lowland site (p < 0.05), whereas the FA profile was unexpectedly similar across sites. Various interactions were found among diet type, cow type and altitude (site) indicating that a combination of these factors contributes to the characteristic FA profile of the respective milk.     

Effects of flaxseed,raw soybeans and calcium salts of fatty acids on apparent total tract digestibility,energy balance and milk fatty acid profile of transition cows

Oilseeds offer some protection to the access of ruminal microorganisms and may be an alternative to calcium salts of fatty acids (FA), which are not fully inert in the ruminal environment. This study aimed to evaluate the effects of different sources of FA supplementation on apparent total tract nutrient digestibility, milk yield and composition, and energy balance (EB) of cows during the transition period and early lactation. We compared diets rich in C18:2 and C18:3 FA. Multiparous Holstein cows were randomly assigned to receive one of the four diets: control (n=11); whole flaxseed (WF, n=10), 60 and 80 g/kg (diet dry matter (DM) basis) of WF during the prepartum and postpartum periods, respectively; whole raw soybeans (WS, n=10), 120 and 160 g/kg (diet DM basis) of WS during the prepartum and postpartum periods, respectively; and calcium salts of unsaturated fatty acids (CSFA, n=11), 24 and 32 g/kg (diet DM basis) of CSFA during the prepartum and postpartum periods, respectively. Dry cows fed WF had higher DM and net energy of lactation (NE_L) intake than those fed WS or CSFA. The FA supplementation did not alter DM and NDF apparent total tract digestibility, dry cows fed WF exhibited greater NDF total tract digestion than cows fed WS or CSFA. Feeding WS instead of CSFA did not alter NE_L intake and total tract digestion of nutrients, but increased milk fat yield and concentration. Calculated efficiency of milk yield was not altered by diets. FA supplementation increased EB during the postpartum period. Experimental diets increased long-chain FA (saturated and unsaturated FA) in milk. In addition, cows fed WS and CSFA had higher C18:1 trans-11 FA and C18:2 cis, and lower C18:3 FA in milk than those fed WF. Furthermore, cows fed CSFA had higher C18:1 trans-11 and cis-9, trans-11 FA than cows fed WS. Although supplemental C18:2 and C18:3 FA did not influence the milk yield of cows, they positively affected EB and increased unsaturated long-chain FA in milk fat.     

Saturated fat supplemented in the form of triglycerides decreased digestibility and reduced performance of dairy cows as compared to calcium salt of fatty acids

The two most popular rumen-protected fatty acid supplements in dairy cow rations are calcium salts of palm oil fatty acid calcium salts of palm oil fatty acid (CSFA) and prilled saturated fatty acids (SFAs). The objectives of this study were to determine the effects of supplementing SFA in the form of triglycerides (TSFA), as compared to CSFA, on yields, efficiency and diet digestibility in high-yielding dairy cows. Twenty-eight (14 cows in each group) multiparous cows were fed a basal diet supplemented (on DM basis) with either 12 g/kg TSFA (~350 g/cow per day – contained 980 g/kg fat; 882.3 g/kg SFAs) or 14 g/kg CSFA (~440 g/cow per day – contained 800 g/kg fat; 566.4 g/kg SFAs). The supplement amounts in the diet were balanced according to fat content. Rumen samples were taken for measurements of ammonia and volatile fatty acids concentrations, and fecal samples were taken for digestibility measurements. The CSFA cows produced 3% higher milk yields (47.6 v. 46.2 kg/day; P < 0.0001) and 4.7% higher 4% fat-corrected milk (FCM; 44.7 v. 42.7 kg/day; P = 0.02) than the TSFA cows. No difference in milk-fat content was observed, but milk-protein content was higher in the TSFA than CSFA cows. Yields of fat and protein were similar, but lactose yields were higher in TSFA cows. There were no differences in dry matter intake or efficiency calculations between groups. The ruminal ammonia concentrations were similar between groups, whereas acetate concentrations and acetate : propionate ratio were greater for CSFA than TSFA cows. The apparent total-tract digestibility of dry (P < 0.0007) and organic matters (P < 0.0003), fat (P < 0.0001), NDF and ADF (P = 0.02) were lower in the TSFA v. CSFA cows. In conclusion, the CSFA-supplemented cows produced 3% higher milk and 4.7% higher 4% FCM than the TSFA cows. However, TSFA supplementation did not depress milk-protein content. The apparent total-tract digestibility was lower for all dietary components in the TSFA cows, which was probably due to the effects of both degree of saturation and triglyceride form of the TSFA supplement. Considering that diets were balanced according to the fat content of the supplements, the lower yields of milk and FCM observed in the TSFA than CSFA cows were likely due to the lower digestibility of the fat and other nutrients in the TSFA cows, which might have negatively influenced the dietary energy content.     

Predicting grass dry matter intake,milk yield and milk fat and protein yield of spring calving grazing dairy cows during the grazing season

Predicting the grass dry matter intake (GDMI), milk yield (MY) or milk fat and protein yield (milk solids yield (MSY)) of the grazing dairy herd is difficult. Decisions with regard to grazing management are based on guesstimates of the GDMI of the herd, yet GDMI is a critical factor influencing MY and MSY. A data set containing animal, sward, grazing management and concentrate supplementation variables recorded during weeks of GDMI measurement was used to develop multiple regression equations to predict GDMI, MY and MSY. The data set contained data from 245 grazing herds from 10 published studies conducted at Teagasc, Moorepark. A forward stepwise multiple regression technique was used to develop the multiple regression equations for each of the dependent variables (GDMI, MY, MSY) for three periods during the grazing season: spring (SP; 5 March to 30 April), summer (SU; 1 May to 31 July) and autumn (AU; 1 August to 31 October). The equations generated highlighted the importance of different variables associated with GDMI, MY and MSY during the grazing season. Peak MY was associated with an increase in GDMI, MY and MSY during the grazing season with the exception of GDMI in SU when BW accounted for more of the variation. A higher body condition score (BCS) at calving was associated with a lower GDMI in SP and SU and a lower MY and MSY in all periods. A higher BCS was associated with a higher GDMI in SP and SU, a higher MY in SU and AU and a higher MSY in all periods. The pre-grazing herbage mass of the sward (PGHM) above 4 cm was associated with a quadratic effect on GDMI in SP, on MY in SP and SU and on MSY in SU. An increase in daily herbage allowance (DHA) above 4 cm was associated with an increase in GDMI in AU, an increase in MY in SU and AU and MSY in AU. Supplementing grazing dairy cows with concentrate reduced GDMI and increased MY and MSY in all periods. The equations generated can be used by the Irish dairy industry during the grazing season to predict the GDMI, MY and MSY of grazing dairy herds.     

Frequent moving of grazing dairy cows to new paddocks increases the variability of milk fatty acid composition

The aim of this work was to investigate the variations of milk fatty acid (FA) composition because of changing paddocks in two different rotational grazing systems. A total of nine Holstein and nine Montbéliarde cows were divided into two equivalent groups according to milk yield, fat and protein contents and calving date, and were allocated to the following two grazing systems: a long duration (LD; 17 days) of paddock utilisation on a heterogeneous pasture and a medium duration (MD) of paddock utilisation (7 to 10 days) on a more intensively managed pasture. The MD cows were supplemented with 4 kg of concentrate/cow per day. Grazing selection was characterised through direct observations and simulated bites, collected at the beginning and at the end of the utilisation of two subsequent MD paddocks, and at the same dates for the LD system. Individual milks were sampled the first 3 days and the last 2 days of grazing on each MD paddock, and simultaneously also for the LD system. Changes in milk FA composition at the beginning of each paddock utilisation were highly affected by the herbage characteristics. Abrupt changes in MD milk FA composition were observed 1 day after the cows were moved to a new paddock. The MD cows grazed by layers from the bottom layers of the previous paddock to the top layers of the subsequent new paddock, resulting in bites with high organic matter digestibility (OMD) value and CP content and a low fibre content at the beginning of each paddock utilisation. These changes could induce significant day-to-day variations of the milk FA composition. The milk fat proportions of 16:0, saturated FA and branched-chain FA decreased, whereas proportions of de novo-synthesised FA, 18:0, c9-18:1 and 18:2n-6 increased at paddock change. During LD plot utilisation, the heterogeneity of the vegetation allowed the cows to select vegetative patches with higher proportion of leaves, CP content, OMD value and the lowest fibre content. These small changes in CP, NDF and ADF contents of LD herbage and in OMD values, from the beginning to the end of the experiment, could minimally modify the ruminal ecosystem, production of precursors of de novo-synthesised FA and ruminal biohydrogenation, and could induce only small day-to-day variations in the milk FA composition.     

Towards a better understanding of the respective effects of milk yield and body condition dynamics on reproduction in Holstein dairy cows

The overall reproductive performance has decreased over the last decades, involving changes in cyclicity, oestrous behaviour and fertility. High milk yield (MY), low body condition score (BCS) and large body condition (BC) loss have been identified as risk factors. However, these effects are often confounded, as high MY and body lipid reserve mobilization are correlated. The aim of this study was to evaluate the respective effects of MY and BC on post-partum ovarian cyclicity, oestrus and fertility of Holstein cows. This study provides novel information, as MY and BC change were uncoupled in the overall dataset that included 98 lactations and milk progesterone profiles. Cows were assigned to two feeding-level groups: high feed, which achieved high MY and moderate BC loss throughout lactation (8410 kg, -1.17 unit from calving to nadir BCS), and low feed, which limited MY and triggered a large BC loss (5719 kg, -1.54 unit). MY and BC had different effects at different stages of the reproductive process. Cyclicity as well as non-fertilization and early embryo mortality were mainly driven by body lipid reserves, whereas oestrous behaviour and late embryo mortality were related to MY. The results point to possible uncoupling between cyclicity, oestrus and early and late embryo survival allowing compensation along the reproductive process and leading to similar final reproductive performance. In compact calving systems, which require high pregnancy rates within a short period, higher MY strategies appear unsuitable even where BCS is maintained, owing to depressed oestrous behaviour and probably increased late embryo mortality, which delays rebreeding. Similarly, strategies that compromise cyclicity and fertility by excessively low BCS are unsuitable.     

Feed consumption and performance of dairy cows with alternate feedings of grass silage and maize silage

A feeding experiment was conducted with 10 dairy cows of the Fleckvieh breed and the cross Red Holstein Friesian × Fleckvieh, to study whether feeding with grass silage at the morning meal and maize silage at the evening meal (treatment B: alternating forage allocation) affects forage intake and milk production, in comparison with combined feeding with these two silages at each meal (treatment A). In order to prevent a selective forage consumption in treatment A, the two silages were given as a homogeneous mixture of nearly equal portions (51.6% maize silage, 48.4% grass silage) of dry matter (DM). The experiment was of switch-back design, with the treatment sequences ABA and BAB, and three experimental periods of 6 weeks.The daily forage consumption averaged 12.3 kg DM when the silages were given as a mixture and was significantly higher than the total forage consumption of 11.8 kg DM (P < 0.05) during the alternating allocation of the silages. In treatment B, daily intake of maize silage (7.10 kg DM) was greater than that of grass silage (4.70 kg DM/day). Furthermore, variation between cows in forage intake was significantly higher in this treatment than in treatment A. Average daily milk yield for treatment A was 18.75 kg with 3.84% fat and 3.70% protein, and 18.10 kg with 3.76% fat and 3.68% protein for treatment B. Production was significantly higher (P < 0.05), by 0.65 kg milk or 0.90 kg FCM, for treatment A.     

Adaptation and evaluation of the GrazeIn model of grass dry matter intake and milk yield prediction for grazing dairy cows

The prediction of grass dry matter intake (GDMI) and milk yield (MY) are important to aid sward and grazing management decision making. Previous evaluations of the GrazeIn model identified weaknesses in the prediction of GDMI and MY for grazing dairy cows. To increase the accuracy of GDMI and MY prediction, GrazeIn was adapted, and then re-evaluated, using a data set of 3960 individual cow measurements. The adaptation process was completed in four additive steps with different components of the model reparameterised or altered. These components were: (1) intake capacity (IC) that was increased by 5% to reduce a general GDMI underprediction. This resulted in a correction of the GDMI mean and a lower relative prediction error (RPE) for the total data set, and at all stages of lactation, compared with the original model; (2) body fat reserve (BFR) deposition from 84 days in milk to next calving that was included in the model. This partitioned some energy to BFR deposition after body condition score nadir had been reached. This reduced total energy available for milk production, reducing the overprediction of MY and reducing RPE for MY in mid and late lactation, compared with the previous step. There was no effect on predicted GDMI; (3) The potential milk curve was reparameterised by optimising the rate of decrease in the theoretical hormone related to secretory cell differentiation and the basal rate of secretory cell death to achieve the lowest possible mean prediction error (MPE) for MY. This resulted in a reduction in the RPE for MY and an increase in the RPE for GDMI in all stages of lactation compared with the previous step; and (4) finally, IC was optimised, for GDMI, to achieve the lowest possible MPE. This resulted in an IC correction coefficient of 1.11. This increased the RPE for MY but decreased the RPE for GDMI compared with the previous step. Compared with the original model, modifying this combination of four model components improved the prediction accuracy of MY, particularly in late lactation with a decrease in RPE from 27.8% in the original model to 22.1% in the adapted model. However, testing of the adapted model using an independent data set would be beneficial and necessary to make definitive conclusions on improved predictions.     

Effects of mixtures of red clover and maize silages on the partitioning of dietary nitrogen between milk and urine by dairy cows

Eight multiparous lactating Holstein-Friesian cows were used to evaluate the partitioning of dietary nitrogen (N) from diets based on mixtures of red clover and maize silages in comparison with diets based on ryegrass silage. All cows received 4 kg/day of a standard dairy concentrate with one of four forage treatments in an incomplete changeover design with three 4-week periods. Three treatments were based on mixtures of red clover and maize silage. N intake was altered both by varying the ratio of these silages (40/60 and 25/75 on a dry matter (DM) basis) and by an additional treatment for which the DM intake of the 40/60 mixture was restricted to the level achieved with grass silage. Rumen passage rates were estimated from faecal excretion curves following a pulse oral dose of Dysprosium-labeled silage and urinary excretion of purine derivatives (PD) was used as an index of rumen microbial protein synthesis. Red clover silage mixtures led to significantly increased feed intake (21.5, 20.7 and 15.2 kg DM/day for 40/60 and 25/75 red clover/maize silage mixtures and grass silage, respectively), milk production (25.8, 27.8 and 20.0 kg/day for the same treatments, respectively) and milk component yields, but were without effect on milk fat and protein concentrations. The large increase in the yield of milk (24.5 kg/day) and milk components for the restricted red clover/maize silage treatment, in comparison with the grass silage treatment, was proportionately greater than the increase in DM intake (16.6 kg DM/day). There were no significant treatment effects on diet digestibility, while the higher intakes of red clover silage mixtures were associated with higher rumen passage rates (5.82%, 6.24% and 4.55%/h, respectively). There were significant effects of both N intake and forage source on the partitioning of dietary N between milk and urine. When dietary protein was diluted by the inclusion of maize silage, red clover silage led to increased milk N and reduced urinary N in comparison with grass silage. Improvements in N utilisation may be related to increased dietary starch and/or rumen passage rates leading to increased microbial protein synthesis for these treatments. Urinary excretion of PD was significantly higher for all diets based on mixtures of red clover and maize silages, in comparison with grass silage. Urinary N output was close to literature predictions based on N intake for the diet based on ryegrass silage, but 40 to 80 g/day (25% to 30%) less than predicted for the diets based on the mixtures of red clover and maize silages.