Estrogen concentrations in milk at estrus and ovulation in dairy cows

The aim of the present study was two-fold. First, to characterize the secretory profiles of oestradiol-17beta and progesterone in relation to the structural changes observed by ultrasonography during follicular dynamics in non-ovulating llamas. Second, to evaluate the effect of exogenous progesterone on follicular activity, in terms of follicle development and hormone production. In experiment one, six adult non-pregnant, non-lactating llamas were examined daily by rectal palpation and transrectal ultrasonography during 70 days. On day 54, intravaginal devices containing 0.33 g of progesterone (CIDR) were inserted and left in the vagina during 16 days. The mean duration of a follicular wave was 22.6+/-2.5 days. The follicular growth phase (follicles growing from 3mm to maximum size) averaged 9.2+/-2.8 days, the mature phase (follicles around maximum size) 5.2+/-1.4 days and regression phase (follicles with decreasing size) 8.2+/-2.2 days. Oestradiol-17beta plasma concentrations exhibited a similar wave pattern (P<0.05). In addition, oestradiol-17beta peak plasma concentrations (46.9+/-3.3 pmoll(-1)) were attained approximately 12 days after the beginning of the growing phase in connection with maximum follicle size (11.8+/-1.6mm). After CIDR insertion, a rapid increase in plasma progesterone concentrations was observed, with peak concentrations attained on day 1 after insertion. Thereafter, concentrations decreased gradually. Mean follicle size steadily decreased from the day of CIDR insertion to day 11 post-insertion (10.3+/-1.6 and 3.3+/-0.8mm, respectively). In order to investigate the effect of follicle size at CIDR insertion on the outcome of progesterone treatment, experiment two was designed. Sixteen adult non-pregnant and non-lactating llamas were divided into four groups according to follicle development at the time of CIDR insertion (group I: follicles < or =6 mm; group II: follicles between 6 and 9 mm; group III: follicles between 10 and 14 mm and group IV, regressing follicles). In groups II, III and IV, a significant decrease in follicle size was observed after the insertion of the CIDR device. In group I, no further development of dominant follicles was observed until the device was withdrawn. In all cases, the smallest diameter was registered between days 5 and 7 after the beginning of treatment. In conclusion, a detailed characterization of follicular waves using ultrasound and hormone determinations simultaneously in non-ovulating llamas and after the insertion of progesterone releasing devices, is presented.     

Effect of butaphosphan and cyanocobalamin on postpartum metabolism and milk production in dairy cows

The aim of this study was to determine the effect of butaphosphan and cyanocobalamin (BTPC) supplementation on plasma metabolites and milk production in postpartum dairy cows. A total of fifty-two Holstein cows were randomly assigned to receive either: (1) 10 ml of saline (NaCl 0.9%, control group); (2) 1000 mg of butaphosphan and 0.5 mg of cyanocobalamin (BTPC1 group); and (3) 2000 mg of butaphosphan and 1.0 mg of cyanocobalamin (BTPC2 group). All cows received injections every 5 days from calving to 20 days in milk (DIM). Blood samples were collected every 15 days from calving until 75 DIM to determine serum concentration of glucose, non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHB), cholesterol, urea, calcium (Ca), phosphorus (P), magnesium (Mg), aminotransferase aspartate (AST) and γ-glutamyltransferase (GGT). The body condition score (BCS) and milk production were evaluated from calving until 90 DIM. Increasing doses of BTPC caused a linear reduction in plasma concentrations of NEFA and cholesterol. Supplementation of BTPC also reduced concentrations of BHB but it did not differ between the two treatment doses. Milk yield and milk protein had a linear increase with increasing doses of BTPC. A quadratic effect was detected for milk fat and total milk solids according to treatment dose, and BTPC1 had the lowest mean values. Concentrations of glucose, urea, P, Mg, AST, GGT, milk lactose and BCS were not affected by treatment. These results indicate that injections of BTPC during the early postpartum period can reduce NEFA and BHB concentrations and increase milk production in Holstein cows.     

Control of estrus and ovulation in dairy cows

The efficiency of a synthetic prostaglandin analog (ICI 80996) for the control of the estrus cycle in dairy cows has been tested with and without simultaneous use of progestagen implants (SC 21009, Searle). Synchronization of estrus is closer after combined progestagen-prostaglandin treatments than after prostaglandins alone (78.7 % in estrus in 48h vs 60.2 % ; P<0.001).The percentage of cows not observed in estrus during the first 96h after the end of treatment was also lower after combined treatments (20.7 % vs 31.8 % ; P<0.05). The best estrus synchronization was obtained by injecting prostaglandin analog two days before implant removal (86 % in estrus in 48h and 14.0 % not observed in estrus within 96h).Fertility was studied in a field trial after one or two inseminations at a predetermined time for each treatment. A higher pregnancy rate was obtained with two inseminations after combined progestagen-prostaglandin treatment (49.1 %). This pregnancy rate differed significantly (P<0.05) from those obtained with one A.I. after the same treatment or two A.I. after the prostaglandin treatment but did not differ from the pregnancy rate obtained with one A.I. 80h after the second prostaglandin injection. The most important problem in dairy cows is the fall in pregnancy rate between 21 days and 6 months (19.7 to 35.1 % depending on treatment ; P<0.05).     

Effect of grain and forage fractions of corn silage on milk production and composition in dairy cows

Corn silage (CS) is associated with a reduction in milk fat content. The fact that CS is constituted of a grain and a forage fraction could explain this effect. This experiment evaluated the effect of grain fraction of CS on rumen fermentation, production performance and milk composition. Earless CS (ECS) was harvested after manually removing corn ears from the plant. Whole CS (WCS) was harvested from the same field on the same day. Eight (four ruminally fistulated) multiparous Holstein cows (84 days in milk) were utilized in a double 4 × 4 Latin square with 21-day periods. Treatments were (dry matter (DM) basis) (1) 23.0% WCS; (2) 12.4% ECS plus 10.6% high moisture corn (HMC) to obtain reconstituted CS (RCS); (3) 23.0% ECS; and (4) 23.0% timothy silage (TS). Diets were formulated to be isonitrogenous and were fed as total mixed ration once a day. DM intake (DMI), milk yield, 4.0% fat-corrected milk (FCM), as well as protein concentration and yield were higher for WCS than ECS. Compared with WCS, cows tended to eat less with RCS, and produced less milk and milk protein. However, yield of FCM was similar between WCS and RCS. Milk fat concentration and yield, as well as the specific ratio of t11 18:1 to t10 18:1 in milk fat did not differ among diets. Milk urea-N tended to be higher for ECS than WCS and TS, whereas ruminal NH₃-N was higher with ECS than TS. Rumen pH decreased linearly with time after feeding but was not different between treatments. Higher acetate and lower propionate concentration resulted in greater acetate to propionate ratio with ECS compared with WCS. In conclusion, removing grain fraction from CS decreased milk production and modified rumen fermentation without affecting milk fat concentration and yield. Moreover, despite some differences in DMI and total ruminal volatile fatty acid concentration between WCS and RCS, the restoration of FCM yield, using HMC in RCS diets, to a level of production similar to WCS highlights the importance of energy and nutrients supplied by the grain fraction of CS to support milk yield.     

Genetic merit for milk production and reproductive success in dairy cows

The effect of genetic merit for milk production traits - fat, protein and milk yield - in dairy cows on milk production, body condition, blood metabolites, reproductive hormones, feed intake and reproductive performance was studied over a period of 2 years. Cows were grouped into two categories, based on calculated pedigree indices using multiple-trait across country evaluation (MACE). Cows of high genetic merit (HGM, n = 48 in year 1 and n = 46 in year 2) had a mean predicted difference +/- standard deviation for milk production of 475 +/- 76kg. The cows of medium genetic merit (MGM, n = 48 in both years) had a mean predicted difference for milk production of 140 +/- 68kg.The cows calved between January and April, and were offered grass silage ad libitum plus 9kg concentrates per cow per day, irrespective genetic merit, from calving to turnout in March, when they were subjected to one of three grazing systems. Cows were available for rebreeding from late April until late July of each year.High genetic merit cows had higher milk production, incurred greater body condition loss between calving and first service and had lower plasma glucose and insulin-like growth factor-1 (IGF-1) concentrations than medium genetic merit cows. Furthermore, HGM cows had lower first and second service and overall conception rates, and required more services per conception than the MGM cows.Cows that did not conceive to first service were retrospectively compared to those that conceived to first service within each genetic merit group. There were no significant differences between the HGM cows that did not conceive to first service and those that conceived to this service in terms of milk production, body condition score change between calving and first service, feed intake at first service, or in plasma concentrations of glucose, non-esterified fatty acids (NEFA) or IGF-1. Medium genetic merit cows that did not conceive to first service lost more body condition between calving and first service than did those that conceived to this service.In the present study, HGM cows had higher milk production and reduced reproductive performance in comparison with MGM cows. However, reproductive performance was not associated with milk production, feed intake or plasma concentrations of glucose, NEFA or IGF-1 between calving and first service, since there were no significant differences in these variates between high or medium genetic merit cows that did not conceive to first service and those that conceived to this service. Therefore, these variates are unlikely to be useful predictors of reproductive performance, under the conditions of the present study.     

Effect of postpartum suppression of ovulation on uterine involution in dairy cows

The objective of this study was to investigate the effect of time of first postpartum ovulation after calving on uterine involution in dairy cows with and without uterine puerperal disease. Transvaginal follicular puncture (FP) of follicles >6 mm suppressed ovulation and development of a CL until Day 42 after calving. Fifty-three lactating Holstein Friesian cows (3.4 ± 1.2 years old, parity 2.5 ± 1.0 [median ± mean absolute deviation]) were divided into groups on the basis of the presence (UD+) or absence (UD−) of uterine disease and whether FP was carried out (FP+) or not (FP−). Uterine disease was defined as the occurrence of retained fetal membranes and/or metritis. This resulted in the following groups: UD−FP− (n = 15), UD−FP+ (n = 13), UD+FP− (n = 13), and UD+FP+ (n = 12). A general examination, vaginoscopy, transrectal palpation, and transrectal B-mode sonography of the reproductive organs were conducted on Days 8, 11, 18, and 25 and then every 10 days until Day 65 after calving. After hormonal synchronization of ovulation (cloprostenol between Days 55 and 60 postpartum and GnRH 2 days later), cows were inseminated in the next spontaneous estrus. On average, the cows ovulated on Day 21.0 ± 6.0 (UD−FP−), 50.0 ± 4.0 (UD−FP+), 16.0 ± 3.0 (UD+FP−), and 48.0 ± 2.0 (UD+FP+) postpartum. Calving-to-conception interval and first-service conception rates were not affected by FP (P > 0.05). Healthy cows with FP had smaller (P < 0.05) uterine horn and cervical diameters assessed sonographically than cows without FP. FP reduced the prevalence of purulent vaginal discharge and uterine size assessed transrectally in UD+ cows (P < 0.05). The results showed that suppression of an early ovulation by transvaginal FP improved uterine involution in cows with and without uterine disease.     

Effect of yeast culture on milk production and metabolic and reproductive performance of early lactation dairy cows

Background

The main objective of this study was to estimate the effect of supplementation with Saccaromyces cerevisiae (SC) (Yea-Sacc^® 1026) on milk production, metabolic parameters and the resumption of ovarian activity in early lactation dairy cows.

Methods

The experiment was conducted during 2005/2006 in a commercial tied-house farm with an average of 200 milking Estonian Holstein Friesian cows. The late pregnant multiparous cows (n = 46) were randomly divided into two groups; one group received 10 g yeast culture from two weeks before to 14 weeks after calving. The groups were fed a total mixed ration with silages and concentrates. Milk recording data and blood samples for plasma metabolites were taken. Resumption of luteal activity was determined using milk progesterone (P₄) measurements. Uterine bacteriology and ovarian ultrasonography (US) were performed and body condition scores (BCS) and clinical disease occurrences were recorded. For analysis, the statistical software Stata 9.2 and R were used to compute Cox proportional hazard and linear mixed models.

Results

The average milk production per cow did not differ between the groups (32.7 ± 6.4 vs 30.7 ± 5.3 kg/day in the SC and control groups respectively), but the production of milk fat (P < 0.001) and milk protein (P < 0.001) were higher in the SC group. There was no effect of treatment on BCS. The analysis of energy-related metabolites in early lactation showed no significant differences between the groups. In both groups higher levels of β-hydroxybutyrate (BHB) appeared from days 14 to 28 after parturition and the concentration of non-esterfied fatty acid (NEFA) was higher from days 1–7 post partum (PP). According to US and P₄ results, all cows in both groups ovulated during the experimental period. The resumption of ovarian activity (first ovulations) and time required for elimination of bacteria from the uterus did not differ between the groups.

Conclusion

Supplementation with SC had an effect on milk protein and fat production, but did not influence the milk yield. No effects on PP metabolic status, bacterial elimination from the uterus nor the resumption of ovarian activity were found.

     

Pasture intake and milk production of dairy cows rotationally grazing on multi-species swards

Increasing plant species diversity has been proposed as a means for enhancing annual pasture productivity and decreasing seasonal variability of pasture production facing more frequent drought scenarios due to climate change. Few studies have examined how botanical complexity of sown swards affects cow performance. A 2-year experiment was conducted to determine how sward botanical complexity, from a monoculture of ryegrass to multi-species swards (MSS) (grasses-legumes-forb), affect pasture chemical composition and nutritive value, pasture dry matter (DM) intake, milk production and milk solids production of grazing dairy cows. Five sward species: perennial ryegrass (L as Lolium), white clover and red clover (both referred to as T as Trifolium because they were always sown together), chicory (C as Cichorium) and tall fescue (F as Festuca) were assigned to four grazing treatments by combining one (L), three (LT), four (LTC) or five (LTCF) species. Hereafter, the LT swards are called mixed swards as a single combination of ryegrass and clovers, whereas LTC and LTCF swards are called MSS as a combination of at least four species from three botanical families. The experimental area (8.7 ha) was divided into four block replicates with a mineral nitrogen fertilisation of 75 kg N/ha per year for each treatment. In total, 13 grazing rotations were carried out by applying the same grazing calendar and the same pasture allowance of 19 kg DM/cow per day above 4 cm for all treatments. Clover represented 20% of DM for mixed and MSS swards; chicory represented 30% of DM for MSS and tall fescue represented 10% of DM for LTCF swards. Higher milk production (+1.1 kg/day) and milk solids production (+0.08 kg/day) were observed for mixed swards than for ryegrass swards. Pasture nutritive value and pasture DM intake were unaffected by the inclusion of clover. Pasture DM, organic matter and NDF concentrations were lower for MSS than for mixed swards. Higher milk production (+0.8 kg/day), milk solids production (+0.04 kg/day) and pasture DM intake (+1.5 kg DM/day) were observed for MSS than for mixed swards. These positive effects of MSS were observed for all seasons, but particularly during summer where chicory proportion was the highest. In conclusion, advantages of grazing MSS on cow performance were due to the cumulative effect of improved pasture nutritive value and increased pasture DM intake that raised milk production and milk solids production.     

Body condition score and live-weight effects on milk production in Irish Holstein-Friesian dairy cows

The objective of the present study was to quantify the relationships among body condition score (BCS; scale 1 to 5), live weight (WT) and milk production in Irish Holstein-Friesian spring calving dairy cows. Data were from 66 commercial dairy herds during the years 1999 and 2000. The data consisted of up to 9886 lactations with records for BCS or WT at least once pre-calving, or at calving, nadir or 60 days post-calving. Change in BCS and WT was also calculated between time periods. Mixed models with cow included as a random effect were used to quantify the effect of BCS and WT, as well as change in each trait, on milk yield, milk fat concentration and milk protein concentration. Significant and sometimes curvilinear associations were observed among BCS at calving or nadir and milk production. Total 305-day milk yield was greatest in cows calving at a BCS of 4.25 units. However, cows calving at a BCS of 3.50 units produced only 68 kg less milk than cows calving at a BCS of 4.25 units while cows calving at 3.25 or 3.00 BCS units produced a further 50 and 114 kg less, respectively. Cows that lost more condition in early lactation produced more milk of greater fat and protein concentration, although the trend reversed in cows that lost large amounts of condition post-calving. Milk yield increased with WT although the marginal effect decreased as cows got heavier. Milk fat and protein concentration in early lactation also increased with WT pre-calving, calving and nadir, although WT did not significantly affect average lactation milk fat concentration.     

Effect of exogenous FSH on estrus, ovulation and endogenous hormone release in dairy cows

Fifteen lactating Holstein cows were randomly allotted to receive either 0 mg (group 0), 32 mg (group 1) or 50 mg (group 2) porcine follicle stimulating hormone (FSH-P) injected in 10 fractions at 12 hr intervals beginning on day 9 of the estrous cycle. All cows received 25 mg prostaglandin (PG) on day 11. Jugular blood samples were collected from cows in all groups at 6 hr intervals beginning on day 7 and continuing through expression of estrus. Mean duration to occurrence of estrus and preovulatory LH surge after PG injection was reduced (P<.05) by injection of FSH-P. Mean number of ovulations increased (P<.05) progressively with increased dose of FSH-P. Mean peripheral progesterone declined more uniformly in FSH-P treated cows after PG and increased earlier (P<.05) after estrus in group 2 cows compared to group 0 and 1 cows. Mean plasma estradiol-17beta elevated (P<.05) after PG injection in both FSH-P-treated groups compared to group 0 cows. Both LH and FSH increased (P<.05) for 36 hr after initiation of FSH-P injection in groups 1 and 2, then declined until after PG injection. Peak LH and FSH occurred more uniformly following PG in treated cows. Results indicate that FSH-P increased endogenous gonadotropin release, estradiol-17beta, ovulation rate and reduced duration to estrus and preovulatory gonadotropin release after PG. Injection of 50 mg FSH-P increased plasma estradiol-17beta and ovulation rate compared to injection of 32 mg FSH-P.     

Effect of lactation trimester and parity on eating behavior,milk production and efficiency traits of dairy cows

There is absence knowledge about the effects of lactation trimester and parity on eating behavior, production and efficiency of dairy cows. Objective of this study was to identify and characterize in 340 dairy cows, the 20% high efficient (HE), 20% low efficient (LE) and 60% mid efficient (ME) cows according to their individual residual feed intake (RFI) values, within and between lactation trimesters and between 1st and 2nd parities. Efficiency effect within each lactation trimester, was exhibited in daily dry matter intake (DMI), eating rate and meal size, that were the highest in LE cows, moderate in the ME cows and lowest in the HE group. Daily eating time, meal frequency, yields of milk and energy-corrected milk (ECM) and BW were similar in the three efficiency groups within each trimester. The lower efficiency of the LE cows in each trimester attributes to their larger metabolic energy intake, heat production and energy losses. In subgroup of 52 multiparous cows examined along their 1st and 2nd trimesters, milk and ECM production, DMI, eating behavior and efficiency traits were similar with high Pearson’s correlation (r=0.78 to 0.89) between trimesters. In another subgroup of 42 multiparous cows measured at their 2nd and 3rd trimesters, milk and ECM yield, DMI and eating time were reduced (P<0.01) at the 3rd trimester, but eating rate, meal frequency and meal size remained similar with high Pearson’s correlation (r=0.74 to 0.88) between trimesters. In subgroup of 26 cows measured in 1st and 2nd parities, DMI, BW, milk and ECM yield, and ECM/DMI increased in the 2nd lactation, but eating behavior and RFI traits were similar in both parities. These findings encourage accurate prediction of DMI based on a model that includes eating behavior parameters, together with individual measurement of ECM production. This can be further used to identify HE cows in commercial herd, a step necessary for potential genetic selection program aimed to improve herd efficiency.     

Relationships among serum lipids,milk production and physiological status in dairy cows

• 1.1. Serum concentrations of cholesterol, triglyceride and alpha lipoprotein cholesterol were determined in nine Holstein cows during different stages of their gestation and lactation cycles.
• 2.2. Serum cholesterol concentrations and daily milk yields were significantly correlated during early and late lactation. The correlations were not significant over the entire lactation.
• 3.3. Maximum values for serum cholesterol were observed at mid lactation and minimum at or near parturition. Serum triglyceride concentrations ranged from 4 to 33 mg/dl. Although prepartum levels for triglyceride tended to be higher than postpartum concentrations, no correlation with milk yield was noted.
• 4.4. These data are compared with lipid changes which take place in other mammals during lactation.

     

Associations among milk production and rectal temperature on pregnancy maintenance in lactating recipient dairy cows

The objective of this study was to evaluate the associations among milk production, rectal temperature, and pregnancy maintenance in lactating recipient dairy cows. Data were collected during an 11-mo period from 463 Holstein cows (203 primiparous and 260 multiparous) assigned to a fixed-time embryo transfer (ET) protocol. Only cows detected with a visible corpus luteum immediately prior to ET were used. Rectal temperatures were collected from all cows on the same day of ET. Milk production at ET was calculated by averaging individual daily milk production during the 7d preceding ET. Pregnancy diagnosis was performed by transrectal ultrasonography 21d after ET. Cows were ranked and assigned to groups according to median milk production (median=35kg/d; HPROD=above median; LPROD=below median) and rectal temperature (≤39.0°C=LTEMP; >39.0°C=HTEMP). A milk production×temperature group interaction was detected (P=0.04) for pregnancy analysis because HTEMP cows ranked as LPROD were 3.1 time more likely to maintain pregnancy compared with HTEMP cows ranked as HPROD (P=0.03). Milk production did not affect (P=0.55) odds of pregnancy maintenance within LTEMP cows, however, and no differences in odds of pregnancy maintenance were detected between HTEMP and LTEMP within milk production groups (P>0.11). Within HTEMP cows, increased milk production decreased the probability of pregnancy maintenance linearly, whereas within LTEMP cows, increased milk production increased the probability of pregnancy maintenance linearly. Within HPROD, increased rectal temperature decreased the probability of pregnancy maintenance linearly, whereas within LPROD cows, no associations between rectal temperatures and probability of cows to maintain pregnancy were detected. In summary, high-producing dairy cows with rectal temperatures below 39.0°C did not experience reduced pregnancy maintenance to ET compared to cohorts with reduced milk production.     

Relationship between level of milk production and estrous behavior of lactating dairy cows

The objective of this study was to determine if there is an association between level of milk production and duration of estrus as determined by standing activity recorded by a radiotelemetry system. Holstein cows (n = 267; 50 DIM) were fitted with a transmitter that allowed continuous recording of standing activity. Cows were housed in a free-stall barn and milked twice daily. Ovulation was confirmed for all estruses (n = 380). Average milk production for the 10 days before the day of estrus was used to classify cows as lower (< 39.5 kg/day) or higher (>/= 39.5 kg/day) producers at the time of estrous expression. Follicle size and serum estradiol (E(2)) concentrations were determined in a subset of cows (n = 71) on the day of estrus. Duration (6.2 +/- 0.5 h versus 10.9 +/- 0.7 h; P < 0.0001), standing events (6.3 +/- 0.4 versus 8.8 +/- 0.6; P = 0.001), and standing time (21.7 +/- 1.3 s versus 28.2 +/- 1.9 s; P = 0.007) were shorter for estruses from higher (46.4 +/- 0.4 kg/day; n = 146) than lower producers (33.5 +/- 0.3 kg/day; n = 177). Milk production was correlated with the duration of estrus (r = -0.51; P < 0.0001; n = 323). Higher producers had lower E(2) concentrations than lower producers (6.8 +/- 0.5; n = 31 versus 8.6 +/- 0.5 pg/ml; n = 40; P = 0.01) in spite of larger pre-ovulatory follicle diameter (18.6 +/- 0.3; n = 31 versus 17.4 +/- 0.2 mm; n = 40; P 0.004). Interestingly, E(2) concentrations were not correlated with diameter of the pre-ovulatory follicle (r = -0.17; P = 0.15) but milk production was correlated with both E(2) concentrations (r = -0.57; P < 0.0001) and diameter of the pre-ovulatory follicle (r = 0.45; P < 0.0001). Thus, high milk production decreases duration of estrus probably due to decreased circulating concentrations of E(2).     

Effects of rumen-protected choline supplementation on milk production and choline supply of periparturient dairy cows

The objective of the present study was to determine the effects of rumen-protected choline (RPC) supplementation on body condition, milk production and milk choline content during the periparturient period. Thirty-two Holstein cows were allocated into two groups (RPC group - with RPC supplementation, and control group - without RPC supplementation) 28 days before the expected calving. Cows were fed the experimental diet from 21 days before expected calving until 60 days of lactation. The daily diet of the RPC group contained 100 g of RPC from 21 days before calving until calving and 200 g RPC after calving for 60 days of lactation, which provided 25 g and 50 g per day choline, respectively. Body condition was scored on days -21, 7, 35 and 60 relative to calving. Milk production was measured at every milking; milk fat, protein and choline content were determined on days 7, 35 and 60 of lactation. Body condition was not affected by RPC supplementation. Milk yield was 4.4 kg higher for the group of cows receiving supplementary choline during the 60 days experimental period and 4% fat-corrected milk production was also increased by 2.5 kg/day. Milk fat content was not altered by treatment, but fat yield was increased by 0.10 kg/day as a consequence of higher milk yield in the RPC-treated group. Milk protein content tended to increase by RPC supplementation and a 0.18 kg/day significant improvement of protein yield was detected. Milk choline content increased in both groups after calving as the lactating period advanced. However, milk choline content and choline yield were significantly higher in the RPC group than in the control group. The improved milk choline and choline yield provide evidence that some of the applied RPC escaped ruminal degradation, was absorbed from the small intestine and improved the choline supply of the cows and contributed to the changes of production variables.     

Differential effects of oilseed supplements on methane production and milk fatty acid concentrations in dairy cows

It is known that supplementing dairy cow diets with full-fat oilseeds can be used as a strategy to mitigate methane emissions, through their action on rumen fermentation. However, direct comparisons of the effect of different oil sources are very few, as are studies implementing supplementation levels that reflect what is commonly fed on commercial farms. The objective was to investigate the effect of feeding different forms of supplemental plant oils on both methane emissions and milk fatty acid (FA) profile. Four multiparous, Holstein-Friesian cows in mid-lactation were randomly allocated to one of four treatment diets in a 4×4 Latin square design with 28-day periods. Diets were fed as a total mixed ration with a 50 : 50 forage : concentrate ratio (dry matter (DM) basis) with the forage consisting of 75 : 25 maize silage : grass silage (DM). Dietary treatments were a control diet containing no supplemental fat, and three treatment diets containing extruded linseed (EL), calcium salts of palm and linseed oil (CPLO) or milled rapeseed (MR) formulated to provide each cow with an estimated 500 g additional oil/day (22 g oil/kg diet DM). Dry matter intake (DMI), milk yield, milk composition and methane production were measured at the end of each experimental period when cows were housed in respiration chambers for 4 days. There was no effect of treatment diet on DMI or milk protein or lactose concentration, but oilseed-based supplements increased milk yield compared with the control diet and milk fat concentration relative to control was reduced by 4 g/kg by supplemental EL. Feeding CPLO reduced methane production, and both linseed-based supplements decreased methane yield (by 1.8 l/kg DMI) and intensity (by 2.7 l/kg milk yield) compared with the control diet, but feeding MR had no effect on methane emission. All the fat supplements decreased milk total saturated fatty acid (SFA) concentration compared with the control, and SFA were replaced with mainly cis-9 18:1 but also trans FA (and in the case of EL and CPLO there were increases in polyunsaturated FA concentration). Supplementing dairy cow diets with these oilseed-based preparations affected milk FA profile and increased milk yield. However, only the linseed-based supplements reduced methane production, yield or intensity, whereas feeding MR had no effect.     

Dietary influence on protein level in milk and milk yield in dairy cows

Diet can influence the yield of milk protein more than it can influence milk protein content. Providing sufficient dietary crude protein in forms that will maximize amounts of amino acids required for milk protein synthesis to the gastrointestinal tract, in forms that can be digested and absorbed, will provide for optimal milk protein yield and content. Maximizing ruminal microbial protein synthesis is an important part of this strategy. The rest of the strategy involves providing sufficient amounts of the remaining required amino acids as ruminally protected proteins, or amino acids in forms that can be digested in the gastrointestinal tract. A diet deficient in protein will reduce milk protein content 1 to 2 g kg⁻¹ and may substantially reduce yields of milk and milk protein. A diet containing high amounts of readily fermentable carbohydrates may increase milk protein content 1 to 2 g kg⁻¹, and may increase yields of milk and protein, but may also result in digestive and metabolic upsets. Diets containing supplemental fat will increase yield of milk protein, but not as extensively as the increase in yield of milk, because milk protein content is usually reduced 1 to 2 g kg⁻¹. The increased efficiency of milk fat and lactose synthesis is likely to be the reason for this depression in milk protein content. A means of overcoming this problem is a continuing research challenge.     

Effect of low winter temperatures on milk production of dairy cows grazed on farms in a warm temperate climate (Australia)

Two-day milk production figures for dairymen at Armidale (31° S Lat.) and Goulburn (35° S Lat.), Australia, were compared with minimum daily temperatures. Comparisons were made between production levels on days with temperatures above and below 0°C, and between days with varying intensities of cold: differences in production were minor. The infrequent, more prolonged periods of cold weather (cold being days on which the minimum temperature was below 0°C) were also associated with only very slight reductions in milk output; and the most pronounced decline in production was not attributable to low temperatures. Although short-term fluctuations in output were not related to low temperature events or low temperatures in combination with rain, thermal stress on plant growth during winter contributed to a seasonal downturn in production and below-average annual milk yields in areas with low winter temperatures.