Divergence for residual feed intake of Holstein-Friesian cattle during growth did not affect production and reproduction during lactation

Residual feed intake (RFI) is the difference between actual and predicted dry matter intake (DMI) of individual animals. Recent studies with Holstein-Friesian calves have identified an ~20% difference in RFI during growth (calf RFI) and these groups remained divergent in RFI during lactation. The objective of the experiment described here was to determine if cows selected for divergent RFI as calves differed in milk production, reproduction or in the profiles of BW and body condition score (BCS) change during lactation, when grazing pasture. The cows used in the experiment (n=126) had an RFI of −0.88 and +0.75 kg DM intake/day for growth as calves (efficient and inefficient calf RFI groups, respectively) and were intensively grazed at four stocking rates (SR) of 2.2, 2.6, 3.1 and 3.6 cows/ha on self-contained farmlets, over 3 years. Each SR treatment had equal number of cows identified as low and high calf RFI, with 24, 28, 34 and 40/11 ha farmlet. The cows divergent for calf RFI were randomly allocated to each SR. Although SR affected production, calf RFI group (low or high) did not affect milk production, reproduction, BW, BCS or changes in these parameters throughout lactation. The most efficient animals (low calf RFI) lost similar BW and BCS as the least efficient (high calf RFI) immediately post-calving, and regained similar BW and BCS before their next calving. These results indicate that selection for RFI as calves to increase efficiency of feed utilisation did not negatively affect farm productivity variables (milk production, BCS, BW and reproduction) as adults when managed under an intensive pastoral grazing system.     

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.     

Visceral organ weights,digestion and carcass characteristics of beef bulls differing in residual feed intake offered a high concentrate diet

This study examined the relationship of residual feed intake (RFI) with digestion, body composition, carcass traits and visceral organ weights in beef bulls offered a high concentrate diet. Individual dry matter (DM) intake (DMI) and growth were measured in a total of 67 Simmental bulls (mean initial BW 431 kg (s.d.=63.7)) over 3 years. Bulls were offered concentrates (860 g/kg rolled barley, 60 g/kg soya bean meal, 60 g/kg molasses and 20 g/kg minerals per vitamins) ad libitum plus 0.8 kg grass silage DM daily for 105 days pre-slaughter. Ultrasonic muscle and fat depth, body condition score (BCS), muscularity score, skeletal measurements, blood metabolites, rumen fermentation and total tract digestibility (indigestible marker) were determined. After slaughter, carcasses and perinephric and retroperitoneal fat were weighed, carcasses were graded for conformation and fat score and weight of non-carcass organs, liver, heart, kidneys, lungs, gall bladder, spleen, reticulo-rumen full and empty and intestines full, were determined. The residuals of the regression of DMI on average daily gain (ADG), mid-test metabolic BW (BW^0.75) and the fixed effect of year, using all animals, were used to compute individual RFI coefficients. Animals were ranked on RFI and assigned to high (inefficient), medium or low groupings. Overall mean ADG and daily DMI were 1.6 kg (s.d.=0.36) and 9.4 kg (s.d.=1.16), respectively. High RFI bulls consumed 7 and 14% more DM than medium and low RFI bulls, respectively (P<0.001). No differences between high and low RFI bulls were detected (P>0.05) for ADG, BW, BCS, skeletal measurements, muscularity scores, ultrasonic measurements, carcass weight, perinephric and retroperitoneal fat weight, kill-out proportion and carcass conformation and fat score. However, regression analysis indicated that a 1 kg DM/day increase in RFI was associated with a decrease in kill-out proportion of 20 g/kg (P<0.05) and a decrease in carcass conformation of 0.74 units (P<0.05). Weight of non-carcass organs did not differ (P>0.05) between RFI groups except for the empty weight of reticulo-rumen, which was 8% lighter (P=0.05) in low RFI compared with high RFI bulls. Regression analysis indicated that a 1 kg DM/day increase in RFI was associated with a 1 kg increase in reticulo-rumen empty weight (P<0.05). Of the visceral organs measured, the reticulo-rumen may be a biologically significant contributory factor to variation in RFI in beef bulls finished on a high concentrate diet.     

Developing and validating a model to predict the dry matter intake of grazing lactating beef cows

Current techniques for measuring the dry matter intake (DMI) of grazing lactating beef cows are invasive, time consuming and expensive making them impractical for use on commercial farms. This study was undertaken to explore the potential to develop and validate a model to predict DMI of grazing lactating beef cows, which could be applied in a commercial farm setting, using non-invasive animal measurements. The calibration dataset used to develop the model was comprised of 94 measurements recorded on 106 beef or beef–dairy crossbred cows (maternal origin). The potential of body measurements, linear type scoring, grazing behaviour and thermal imaging to predict DMI in combination with known biologically plausible adjustment variables and energy sinks was investigated. Multivariable regression models were constructed for each independent variable using SAS PROC REG and contained milk yield, BW, parity, calving day and maternal origin (dairy or beef). Of the 94 variables tested, 32 showed an association with DMI (P < 0.25) upon multivariable analysis. These variables were incorporated into a backwards linear regression model using SAS PROC REG. Variables were retained in this model if P < 0.05. Five variables; width at pins, full body depth, ruminating mastications, central ligament and rump width score, were retained in the model in addition to milk yield, BW, parity, calving day and maternal origin. The inclusion of these variables in the model increased the predictability of DMI by 0.23 (R² = 0.68) when compared to a model containing milk yield, BW, parity, calving day and maternal origin only. This model was applied to data recorded on an independent dataset; a herd of 60 lactating beef cows two years after the calibration study. The R² for the validation was 0.59. Estimates of DMI are required for measuring feed efficiency. While acknowledging challenges in applicability, the findings suggest a model such as that developed in this study may be used as a tool to more easily and less invasively estimate DMI on large populations of commercial beef cows, and therefore measure feed efficiency.     

Effects of dry period length on milk production and energy balance in two cow breeds

Shortening the dry period (DP) has been proposed as a strategy to improve energy balance (EB) in cows in early lactation. This study evaluated the effects of shortening the DP on milk yield (MY), EB and residual feed intake (RFI) in two breeds; Swedish Red (SR) and Swedish Holstein (SH). Cows were blocked by breed and parity and then randomly assigned to one of two treatments; short DP of 4 weeks (4W, n=43) or conventional DP of 8 weeks (8W, n=34). Cows were kept and fed under the same conditions, except for the 4 weeks when the 4W group were still lactating prepartum and thus kept with the lactating cows. Milk yield and BW were recorded and body condition score (BCS) was rated from 10 weeks prepartum to 12 weeks postpartum. Dry matter intake (DMI) was recorded for lactating cows postpartum. Milk yield was reduced by 6.75 kg/day during the first 12 weeks postpartum (P<0.001) for the 4W cows compared with 8W cows, but there was no significant difference in total MY (3724 kg compared with 3684 kg, P=0.7) when the milk produced prepartum was included. Protein content was higher in 4W cows (3.42%) than in 8W cows (3.27%) (P<0.001) postpartum. In the 8W group, cows lost more BCS after calving (P<0.05). Cows of SR breed had higher BCS than cows of SH breed (SR=3.7, SH=3.2, P<0.001), but no differences in BW were found between breed and treatment. Energy balance was improved for cows in the 4W group (P<0.001), while feed efficiency, expressed as RFI, was reduced for 4W cows than for 8W cows (5.91 compared with −5.39, P<0.01). Shortening the DP resulted in improved EB postpartum with no difference between the breeds and no milk losses when including the milk produced prepartum.     

Effect of rumen-protected methionine supplementation to beef cows during the periconception period on performance of cows,calves, and subsequent offspring

Maternal nutrition affects the development of the fetus and postnatal performance of the calf. Methionine may play a critical role in developmental programming and is likely deficient in beef cows fed low-quality forage. The objective of this study was to determine the effect of metabolizable methionine supply to lactating beef cows during the periconception period on performance of cows, calves, and subsequent offspring. This project involved two consecutive production cycles commencing at calving in which dietary treatments were fed to cows during the periconception period along with measurements on cows and initial calves in Production Cycle 1, and measurements on subsequent calves in Production Cycle 2. Brangus-Angus crossbred lactating beef cows (N = 108; age = 6.4 (2.8) year) were stratified by previous calving date and assigned to one of three supplements: (1) control, molasses plus urea at 2.72 kg/day as fed, (2) fishmeal, 2.27 kg/day molasses plus urea plus 0.33 kg/day as fed of fishmeal, and (3) methionine, 2.72 kg/day of molasses plus urea plus 9.5 g/day of 2-hydroxy-4-(methylthio)-butanoic acid. Cows were fed supplements and low-quality limpograss (Hemarthria altissima) hay while grazing dormant bahiagrass (Paspalum notatum Flüggé) pastures during the 115-day periconception period from December 2014 to April 2015 in Production Cycle 1 only. Body weight change and milk yield of cows were measured during the periconception period in Production Cycle 1. Body weight of calves was measured at birth and weaning in both production cycles. Following weaning in Production Cycle 2, eight subsequent steer calves per treatment were individually housed for a 42-day metabolism experiment. Treatment did not affect (P > 0.10) BW change of cows, but cows fed methionine tended (P = 0.09) to produce more energy-corrected milk than control and fishmeal. Treatment did not affect (P > 0.10) 205-day adjusted weaning weight of calves in either production cycle. During the metabolism experiment, subsequent calves from dams fed fishmeal and methionine gained faster (P < 0.05) and had greater (P < 0.05) gain:feed than control calves. Methionine calves tended (P = 0.06) to have greater apparent total tract NDF and ADF digestibility and lesser (P < 0.05) blood glucose concentration than control and fishmeal calves. These data indicate that maternal methionine supply during the periconception period plays an important role in programming future performance of the offspring.     

Grazed grass herbage intake and performance of beef heifers with predetermined phenotypic residual feed intake classification

Data were collected on 85 Simmental and Simmental × Holstein–Friesian heifers. During the indoor winter period, they were offered grass silage ad libitum and 2 kg of concentrate daily, and individual dry matter intake (DMI) and growth was recorded over 84 days. Individual grass herbage DMI was determined at pasture over a 6-day period, using the n-alkane technique. Body condition score, skeletal measurements, ultrasonic fat and muscle depth, visual muscularity score, total tract digestibility, blood hormones, metabolites and haematology variables and activity behaviour were measured for all heifers. Phenotypic residual feed intake (RFI) was calculated for each animal as the difference between actual DMI and expected DMI during the indoor winter period. Expected DMI was calculated for each animal by regressing average daily DMI on mid-test live weight (LW)^0.75 and average daily gain (ADG) over an 84-day period. Standard deviations above and below the mean were used to group animals into high (>0.5 s.d.), medium (±0.5 s.d.) and low (<0.5 s.d.) RFI. Overall mean (s.d.) values for DMI (kg/day), ADG (kg), feed conversion ratio (FCR) kg DMI/kg ADG and RFI (kg dry matter/day) were 5.82 (0.73), 0.53 (0.18), 12.24 (4.60), 0.00 (0.43), respectively, during the RFI measurement period. Mean DMI (kg/day) and ADG (kg) during the grazing season was 9.77 (1.77) and 0.77 (0.14), respectively. The RFI groups did not differ (P > 0.05) in LW, ADG or FCR at any stage of measurement. RFI was positively correlated (r = 0.59; P < 0.001) with DMI during the RFI measurement period but not with grazed grass herbage DMI (r = 0.06; P = 0.57). Low RFI heifers had 0.07 greater (P < 0.05) concentration of plasma creatinine than high RFI heifers and, during the grazed herbage intake period, spent less time standing and more time lying (P < 0.05) than high RFI heifers. However, low and high RFI groups did not differ (P > 0.05) in ultrasonic backfat thickness or muscle depth, visual muscle scores, skeletal size, total tract digestibility or blood hormone and haematology variables at any stage of the experiment. Despite a sizeable difference in intake of grass silage between low and high RFI heifers during the indoor winter period, there were no detectable differences between RFI groupings for any economically important performance traits measured when animals were offered ensiled or grazed grass herbage.     

Feeding dried distillers grains with solubles to lactating beef cows: impact of excess protein and fat on cow performance,milk production and pre-weaning progeny growth

Multiparous Angus×Simmental cows (n=54, 5.22±2.51 years) with male progeny were fed one of two diets supplemented with either dried distillers grains with solubles (DDGS) or soybean meal (CON), from calving until day 129 postpartum (PP) to determine effects of excess protein and fat on cow performance, milk composition and calf growth. Diets were formulated to be isocaloric and consisted of rye hay and DDGS (19.4% CP; 8.76% fat), or corn silage, rye hay and soybean meal (11.7% CP; 2.06% fat). Cow–calf pairs were allotted by cow and calf age, BW and breed. Cow BW and body condition score (BCS; P⩾0.13) were similar throughout the experiment. A weigh-suckle-weigh was performed on day 64 and day 110±10 PP to determine milk production. Milk was collected on day 68 and day 116±10 PP for analysis of milk components. Milk production was unaffected (P⩾0.75) by dietary treatments. Milk urea nitrogen was increased at both time points in DDGS compared with CON cows (P<0.01). Protein was decreased (P=0.01) and fat was increased (P=0.01) in milk from DDGS compared with CON cows on day 68 PP. Compared to CON, DDGS decreased medium chain FA (P<0.01) and increased long chain FA (P<0.01) at both time points. Saturated FA content of milk was decreased (P<0.01) at both time-points in DDGS compared with CON cows, which resulted in an increase (P<0.01) in monounsaturated and polyunsaturated FA, including cis-9, trans-11 conjugated linoleic acid. Daily gain of the DDGS calves was increased (P=0.01) compared with CON calves, resulting in heavier BW on day 129 (P=0.01). Heavier BW of DDGS calves was maintained through weaning (P=0.01). Timed-artificial insemination (TAI) rates were greater for cows fed DDGS compared with cows fed CON (P<0.02), but dietary treatment had no effect on overall pregnancy rates (P=0.64). In summary, feeding DDGS to lactating beef cows did not change cow BW or BCS, but did improve TAI rates and altered milk composition compared with CON. As a result, male progeny from cows fed DDGS during lactation had greater average daily gain and were heavier at day 129 and at weaning compared with male progeny from cows fed a control diet.     

The repeatability of feed intake and feed efficiency in beef cattle offered high-concentrate,grass silage and pasture-based diets

Breeding values for feed intake and feed efficiency in beef cattle are generally derived indoors on high-concentrate (HC) diets. Within temperate regions of north-western Europe, however, the majority of a growing beef animal’s lifetime dietary intake comes from grazed grass and grass silage. Using 97 growing beef cattle, the objective of the current study was to assess the repeatability of both feed intake and feed efficiency across 3 successive dietary test periods comprising grass silage plus concentrates (S+C), grazed grass (GRZ) and a HC diet. Individual DM intake (DMI), DMI/kg BW and feed efficiency-related parameters, residual feed intake (RFI) and gain to feed ratio (G : F) were assessed. There was a significant correlation for DMI between the S+C and GRZ periods (r = 0.32; P < 0.01) as well as between the S+C and HC periods (r = 0.41; P < 0.001), whereas there was no association for DMI between the GRZ and HC periods. There was a significant correlation for DMI/kg BW between the S+C and GRZ periods (r = 0.33; P < 0.01) and between the S+C and HC periods (r = 0.40; P < 0.001), but there was no association for the trait between the GRZ and HC periods. There was a significant correlation for RFI between the S+C and GRZ periods (r = 0.25; P < 0.05) as well as between S+C and HC periods (r = 0.25; P < 0.05), whereas there was no association for RFI between the GRZ and HC periods. Gain to feed ratio was not correlated between any of the test periods. A secondary aspect of the study demonstrated that traits recorded in the GRZ period relating to grazing bite rate, the number of daily grazing bouts and ruminating bouts were associated with DMI (r = 0.28 to 0.42; P < 0.05 - 0.001), DMI/kg BW (r = 0.36 to 0.45; P < 0.01 - 0.001) and RFI (r = 0.31 to 0.42; P < 0.05 - 0.001). Additionally, the number of ruminating boli produced per day and per ruminating bout were associated with G : F (r = 0.28 and 0.26, respectively; P < 0.05). Results from this study demonstrate that evaluating animals for both feed intake and feed efficiency indoors on HC diets may not reflect their phenotypic performance when consuming conserved forage-based diets indoors or when grazing pasture.     

Biological mechanisms related to differences in residual feed intake in dairy cows

Residual feed intake (RFI), defined as the difference between an animal’s actual feed intake and expected feed intake over a specific period, is an inheritable character of feed conversion efficiency in dairy cows. Research has shown that a lower RFI could improve the profitability of milk production. This study explored variation in RFI by comparing the differences in body size, milk performance, feeding behavior, and serum metabolites in 29 Holstein cows in mid lactation. The cows were selected from a total of 84 animals based on their RFI following feedlot tests. Selected cows were ranked into high RFI (RFI >1 SD above the mean, n=14) and low RFI (RFI<1 SD below the mean, n=15). The low RFI cows (more efficient) consumed 1.59 kg/day less dry matter than the high RFI group (P<0.01), while they produced nearly equal 4% fat-corrected milk. The milk : feed ratio was higher for the low RFI group than for the high RFI group (P<0.05). The levels of milk protein (P<0.01), total solids (P<0.05), and nonfat solids (P<0.05) were also higher for the low RFI group, whereas milk urea nitrogen was lower (P<0.01). The daily feeding duration was shorter for the low RFI group than for the high RFI group (P<0.01). No significant differences were found in levels of glucose, β-hydroxybutyrate, prolactin, insulin, IGF-1, growth hormone or ghrelin, but the level of neuropeptide Y was higher (P<0.01) and levels of leptin and non-esterified fatty acid (P<0.05) were lower for the low RFI group than for the high RFI group. There were substantial differences between cows with different RFI, which might affect the efficiency of milk protein metabolism and fat mobilization.     

Identification of polymorphisms influencing feed intake and efficiency in beef cattle

Feed efficiency is an economically important trait in beef cattle. Net feed efficiency, measured as residual feed intake (RFI), is the difference between actual feed intake and the predicted feed intake required for maintenance and gain of the animal. SNPs that show associations with RFI may be useful quantitative trait nucleotides for marker-assisted selection. This study identified associations between SNPs underlying five RFI QTL on five bovine chromosomes (BTA2, 5, 10, 20 and 29) with measures of dry matter intake (DMI), RFI and feed conversion ratio (FCR) in beef cattle. Six SNPs were found to have effects on RFI (P < 0.05). The largest single SNP allele substitution effect for RFI was -0.25 kg/day located on BTA2. The combined effects of the SNPs found significant in this experiment explained 6.9% of the phenotypic variation of RFI. Not all the RFI SNPs showed associations with DMI and FCR even though these traits are highly correlated with RFI (r = 0.77 and r = 0.62 respectively). This shows that these SNPs may be affecting the underlying biological mechanisms of feed efficiency beyond feed intake control and weight gain efficiency. These SNPs can be used in marker-assisted selection but first it will be important to verify these effects in independent populations of cattle.     

Digestibility contributes to between-animal variation in feed efficiency in beef cows

Residual feed intake (RFI) is an alternative measure of feed efficiency (FE) and is calculated as the difference between actual and expected feed intake. The biological mechanisms underlying animal-to-animal variation in FE are not well understood. The aim of this study was to investigate the digestive ability of beef cows selected for RFI divergence as heifers, using two contrasted diets. Fifteen 4-year-old beef cows were selected from a total of 69 heifers based on their RFI following the feedlot test. The selected heifers were ranked into high-RFI (+ 1.02 ± 0.28, n = 8) and low-RFI (−0.73 ± 0.28, n = 7), and a digestibility trial was performed after their first lactation. Both RFI groups were offered two different diets: 100% hay or a fattening diet which consisted of a DM basis of 67% whole-plant maize silage and 33% high starch concentrates over four experimental periods (two per diet). A diet effect was observed on feed intake and apparent digestibility, whereas no diet × RFI interaction was detected (P > 0.05). Intake and apparent digestibility were higher in cows fed the fattening diet than in those fed the hay diet (P < 0.0001). DM intake (DMI) and organic matter apparent digestibility (OMd) were repeatable and positively correlated between the two subsequent periods of measurements. For the hay and fattening diets, the repeatability between periods was r = 0.71 and r = 0.73 for DMI and r = 0.87 and r = 0.48 for OMd, respectively. Moreover, both intake (r = 0.55) and OMd (r = 0.54) were positively correlated (P < 0.05) between the hay and fattening diets. Significant differences between beef cows selected for divergence in RFI as heifers were observed for digestive traits (P < 0.05), DM and organic matter (OM) apparent digestibility being higher for low-RFI cows. Overall, this study showed that apparent digestibility contributes to between-animal variation in FE in beef cows.     

Mitochondrial abundance and function in muscle from beef steers with divergent residual feed intakes

The objective of this study was to evaluate the relationship between muscle mitochondrial function and residual feed intake (RFI) in growing beef cattle. A 56-day feeding trial was conducted with 81 Angus × Hereford steers (initial BW = 378 ± 43 kg) from the University of California Sierra Foothills Research Station (Browns Valley, CA, USA). All steers were individually fed the same finishing ration (metabolizable energy = 3.28 Mcal/kg DM). Average daily gain (ADG), DM intake (DMI) and RFI were 1.82 ± 0.27, 8.89 ± 1.06 and 0.00 ± 0.55 kg/day, respectively. After the feeding trial, the steers were categorized into high, medium and low RFI groups. Low RFI steers consumed 13.6% less DM (P < 0.05) and had a 14.1% higher G : F ratio (P < 0.05) than the high RFI group. No differences between RFI groups were found in age, ADG or BW (P > 0.10). The most extreme individuals from the low and high RFI groups were selected to assess mitochondrial function (n = 5 low RFI and n = 6 high RFI). Mitochondrial respiration was measured using an oxygraph (Hansatech Instruments Ltd., Norfolk, UK). State 3 and State 4 respiration rates were similar between both groups (P > 0.10). Respiratory control ratios (RCRs, i.e., State 3 : State 4 oxygen uptakes) declined with animal age and were greater in low RFI steers (4.90) as compared to high RFI steers (4.26) when adjusted for age by analysis of covariance (P = 0.003). Mitochondrial complex II activity levels per gram of muscle were 42% greater in low RFI steers than in high RFI steers (P = 0.004). These data suggest that skeletal muscle mitochondria have greater reserve respiratory capacity and show greater coupling between respiration and phosphorylation in low RFI than in high RFI steers.     

Evaluation of production efficiencies at pasture of lactating suckler cows of diverse genetic merit and replacement strategy

Feed costs account for the largest proportion of direct cost within suckler beef production systems. By identifying the cow type with enhanced capability of converting grazed herbage to beef output across lactations, suckler cow systems would become more efficient and sustainable. The objective of this study was to estimate grass DM intake (GDMI) and production efficiency among lactating suckler cows of diverse genetic merit for the national Irish maternal index (Replacement Index) which includes cow efficiency components such as milk yield and feed intake. Data from 131 cows of diverse genetic merit within the Replacement Index, across two different replacement strategies (suckler or dairy sourced), were available over two grazing seasons. Milk yield, GDMI, cow live weight (BW) and body condition score (BCS) were recorded during early, mid and late-lactation, with subsequent measures of production efficiency extrapolated. Genetic merit had no significant effect on any variables investigated, with the exception of low genetic merit (LOW) cows being 22 kg heavier in BW than high genetic merit (HIGH) cows (P < 0.05). Beef cows were 55 kg heavier in BW (P < 0.001), had a 0.31 greater BCS (P < 0.05) and 0.30 Unité Fourragère Lait (UFL) greater energy requirement for maintenance compared to dairy sourced beef × dairy crossbred (BDX) cows (P < 0.001). The BDX had 0.8 kg greater GDMI, produced 1.8 kg more milk (P < 0.001), had a 0.8 UFL greater energy requirement for lactation and produced weanlings that were 17 kg heavier in BW than beef cows (P < 0.05). Subsequent efficiency variables of milk per 100 kg BW (P < 0.001), milk per kg GDMI (P < 0.001) and GDMI per 100 kg BW (P < 0.001) were more favourable for BDX. The correlations examined showed GDMI had moderate positive correlations (P < 0.001) with intake per 100 kg BW, net energy intake per kg milk yield, RFI and intake per 100 kg calf weaning weight but was weakly negatively correlated to milk yield per kg GDMI (P < 0.001). No difference was observed across genetic merit for beef cows for any of the traits investigated. Results from the current study showed that, while contrasting replacement strategies had an effect on GDMI and production efficiency, no main effect was observed on cows diverse in genetic merit for Replacement Index. Nonetheless, utilising genetic indexes in the suckler herd is an important resource for selecting breeding females for the national herd and phenotypic performance generated from this study can be included in future genetic evaluations to improve reliability of genetic values.     

Extended transition milk feeding for 3 weeks improves growth performance and reduces the susceptibility to diarrhea in newborn female Holstein calves

Dairy calves may benefit from extending the duration of feeding transition milk (TM; the subsequent two to six milkings after parturition) to enhance performance and health during early life. The objective of this study was to assess the effect of replacing pasteurized waste milk (non-saleable milk containing antibiotic and/or drug residues) with pasteurized TM for 3 weeks on the growth performance and health of dairy calves. A total of 84 healthy newborn female Holstein calves were blocked by birth order and assigned randomly to 4 treatment groups with partial replacement of pasteurized waste milk by TM (second milkings after parturition) at 0 (0 l/day TM + 6 l/day milk), 0.5 (0.5 l/day TM + 5.5 l/day milk), 1 (1 l/day TM + 5 l/day milk), or 2 l (2 l/day TM + 4 l/day milk) for a 21-day period. From day 22 onward, all calves were fed individually with 6 l/day pasteurized waste milk. Calves were weaned on day 60 and monitored until day 90 of the study. Liquid feed DM intake (DMI) was increased with increasing levels of TM (P = 0.001). Starter feed DMI and total DMI (liquid feed DMI + starter feed DMI) were not affected by the treatment effect. Calves were fed 2 l/day TM gained more BW compared with those in the control group during the postweaning and overall periods. The average daily gain tended (P = 0.06) to be higher in calves fed 2 l/day TM compared with calves fed 0 (+ 65 g/day), 0.5 (+ 53 g/day), or 1 (+ 76 g/day) l/day TM during the preweaning period. Daily weight gain was also higher in calves fed 2 l/day TM compared with calves in the control group during the postweaning (+ 137 g/day; P = 0.04) and overall (+ 89 g/day; P < 0.01) periods, respectively. Calves fed 2 l/day TM had a higher feed efficiency compared with calves in the control group during all studied periods. The calves fed TM2 had a lower chance of having diarrhea compared with other treatment groups. Duration but not the frequency of diarrhea was lower in calves fed TM2 vs TM0 (2.5 vs 4.2 days; P = 0.03). In general, partial replacement of waste milk with TM (2 l/day) may be recommended to feed dairy calves at an early stage of life to support a higher growth rate and health benefits.     

Differential response to stocking rates and feeding by two genotypes of Holstein-Friesian cows in a pasture-based automatic milking system

The throughput of automatic milking systems (AMS) is likely affected by differential traffic behavior and subsequent effects on the milking frequency and milk production of cows. This study investigated the effect of increasing stocking rate and partial mixed ration (PMR) on the milk production, dry matter intake (DMI), feed conversion efficiency (FCE) and use of AMS by two genotypes of Holstein-Friesian cows in mid-lactation. The study lasted 8 weeks and consisted in a factorial arrangement of two genotypes of dairy cattle, United States Holstein (USH) or New Zealand Friesian (NZF), and two pasture-based feeding treatments, a low stocking rate system (2 cows/ha) fed temperate pasture and concentrate, or a high stocking rate system (HSR; 3 cows/ha) fed same pasture and concentrate plus PMR. A total of 28 cows, 14 USH and 14 NZF, were used for comparisons, with 12 cows, six USH and six NZF, also used for tracking of animal movements. Data were analyzed by repeated measure mixed models for a completely randomized design. No differences (P>0.05) in pre- or post-grazing herbage mass, DMI and FCE were detected in response to increases in stocking rate and PMR feeding in HSR. However, there was a significant (P<0.05) grazing treatment×genotype×week interaction on milk production, explained by differential responses of genotypes to changes in herbage mass over time (P<0.001). A reduction (P<0.01) in hours spent on pasture was detected in response to PMR supplementation in HSR; this reduction was greater (P=0.01) for USH than NZF cows (6 v. 2 h, respectively). Regardless of the grazing treatment, USH cows had greater (P=0.02) milking frequency (2.51 v. 2.26±0.08 milkings/day) and greater (P<0.01) milk yield (27.3 v. 16.0±1.2 kg/day), energy-corrected milk (24.8 v. 16.5±1.0 kg/day), DMI (22.1 v. 16.6±0.8 kg/day) and FCE (1.25 v. 1.01±0.06 kg/kg) than NZF cows. There was also a different distribution of milkings/h between genotypes (P<0.001), with patterns of milkings/h shifting (P<0.001) as a consequence of PMR feeding in HSR. Results confirmed the improved FCE of grazing dairy cows with greater milk production and suggested the potential use of PMR feeding as a tactical decision to managing HSR and milkings/day in AMS farms.     

Mitochondrial abundance and function in skeletal muscle and liver from Simmental beef cattle divergent for residual feed intake

Cellular mitochondrial function has been suggested to contribute to variation in feed efficiency (FE) among animals. The objective of this study was to determine mitochondrial abundance and activities of various mitochondrial respiratory chain complexes (complex I (CI) to complex IV (CIV)) in liver and muscle tissue from beef cattle phenotypically divergent for residual feed intake (RFI), a measure of FE. Individual DM intake (DMI) and growth were measured in purebred Simmental heifers (n = 24) and bulls (n = 28) with an initial mean BW (SD) of 372 kg (39.6) and 387 kg (50.6), respectively. All animals were offered concentrates ad libitum and 3 kg of grass silage daily, and feed intake was recorded for 70 days. Residuals of the regression of DMI on average daily gain (ADG), mid-test BW^0.75 and backfat (BF), using all animals, were used to compute individual RFI coefficients. Animals were ranked within sex, by RFI into high (inefficient; top third of the population), medium (middle third of population) and low (efficient; bottom third of the population) terciles. Statistical analysis was carried out using the MIXED procedure of SAS v 9.3. Overall mean ADG (SD) and daily DMI (SD) for heifers were 1.2 (0.4) and 9.1 (0.5) kg, respectively, and for bulls were 1.8 (0.3) and 9.5 (1.02) kg, respectively. Heifers and bulls ranked as high RFI consumed 10% and 15% more (P < 0.05), respectively, than their low RFI counterparts. There was no effect of RFI on mitochondrial abundance in either liver or muscle (P > 0.05). An RFI × sex interaction was apparent for CI activity in muscle. High RFI animals had an increased activity (P < 0.05) of CIV in liver tissue compared to their low RFI counterparts; however, the relevance of that observation is not clear. Our data provide no clear evidence that cellular mitochondrial function within either skeletal muscle or hepatic tissue has an appreciable contributory role to overall variation in FE among beef cattle.     

Quantitative trait loci with effects on feed efficiency traits in Hereford × composite double backcross populations

Two half-sib families of backcross progeny were produced by mating F₁ Line 1 Hereford (L1) × composite gene combination (CGC) bulls with L1 and CGC cows. Feed intake and periodic weights were measured for 218 backcross progeny. These progenies were genotyped using 232 microsatellite markers that spanned the 29 BTA. Progeny from L1 and CGC females was analysed separately using composite interval mapping to find quantitative trait loci (QTL) affecting daily dry matter intake (DMI), average daily gain (ADG), feed conversion (FCR) and residual feed intake (RFI). Results from both backcrosses were pooled to find additional QTL. In the backcross to L1, QTL were detected for RFI and DMI on BTA11, FCR on BTA16, and ADG on BTA9. In the backcross to CGC, QTL were detected for RFI on BTA10, FCR on BTA12 and 16 and ADG on BTA15 and 17. After pooling, QTL were detected for RFI on BTA 2, 6, 7, 10, 11, 13 and 16; for FCR on BTA 9, 12, 16, 17 and 21; for ADG on BTA 9, 14, 15, 17; and for DMI on BTA 2, 5, 6, 9, 10, 11, 20 and 23.     

Methane emissions from two breeds of beef cows offered diets containing barley straw with either grass silage or brewers’ grains

Increasing the concentration of dietary lipid is a promising strategy for reducing methane (CH₄) emissions from ruminants. This study investigated the effect of replacing grass silage with brewers’ grains on CH₄ emissions of pregnant, non-lactating beef cows of two breeds. The experiment was a two×two factorial design comprising two breeds (LIMx, crossbred Limousin; and LUI, purebred Luing) and two diets consisting of (g/kg diet dry matter (DM)) barley straw (687) and grass silage (301, GS), or barley straw (763) and brewers’ grains (226, BG), which were offered ad libitum. Replacing GS with BG increased the acid-hydrolysed ether extract concentration from 21 to 37 g/kg diet DM. Cows (n=48) were group-housed in equal numbers of each breed across two pens and each diet was allocated to one pen. Before measurements of CH₄, individual dry matter intake (DMI), weekly BW and weekly body condition score were measured for a minimum of 3 weeks, following a 4-week period to acclimatise to the diets. CH₄ emissions were subsequently measured on one occasion from each cow using individual respiration chambers. Due to occasional equipment failures, CH₄ measurements were run over 9 weeks giving 10 observations for each breed×treatment combination (total n=40). There were no differences between diets for daily DMI measured in the chambers (9.92 v. 9.86 kg/day for BG and GS, respectively; P>0.05). Cows offered the BG diet produced less daily CH₄ than GS-fed cows (131 v. 156 g/day: P<0.01). When expressed either as g/kg DMI or kJ/MJ gross energy intake (GEI), BG-fed cows produced less CH₄ than GS-fed cows (13.5 v. 16.4 g/kg DMI, P<0.05; 39.2 v. 48.6 kJ/MJ GEI, P<0.01). Breed did not affect daily DMI or CH₄ expressed as g/day, g/kg DMI or kJ/MJ GEI (P>0.05). However, when expressed as a proportion of metabolic BW (BW^0.75), LUI cows had greater DMI than LIMx cows (84.5 v. 75.7 g DMI/kg BW^0.75, P<0.05) and produced more CH₄ per kg BW^0.75 than LIMx cows (1.30 v. 1.05 g CH₄/kg BW^0.75; P<0.01). Molar proportions of acetate were higher (P<0.001) and propionate and butyrate lower (P<0.01) in rumen fluid samples from BG-fed compared with GS-fed cows. This study demonstrated that replacing GS with BG in barley straw-based diets can effectively reduce CH₄ emissions from beef cows, with no suppression of DMI.     

Influence of estrus on dry matter intake,water intake and BW of dairy cows

The objectives of this study were to analyze whether dry matter intake (DMI), water intake (WI) and BW were influenced by estrus. A second objective was to determine whether correlations exist among these traits in non-estrous days. Data collection included 34 Holstein-Friesian cows from the research farm ‘Haus Riswick’ of the Agricultural Chamber North Rhine-Westphalia, Germany. On an individual basis, daily DMI and daily WI were measured automatically by a scale in the feeding trough and a WI monitoring system, respectively. BW was determined by a walk-through scale fitted with two gates – one in front and one behind the scale floor. Data were analyzed around cow’s estrus with day 0 (the day of artificial insemination leading to conception). Means during the reference period, defined as days −3 to −1 and 1 to 3, were compared with the means during estrus (day 0). DMI, WI and BW were affected by estrus. Of all cows, 85.3% and 66.7% had reduced DMI and WI, respectively, on day 0 compared with the reference period. Lower BW was detected in 69.2% of all cows relative to the reference period. During the reference period, average DMI, WI and BW were 23.0, 86.6 and 654.8 kg. A minimum DMI of 20.4 kg and a minimum BW of 644.2 kg were detected on the day of estrus, whereas the minimum WI occurred on the day before estrus. After estrus, DMI, WI and BW returned to baseline values. Intake of concentrated feed did not seem to be influenced by estrus. Positive correlations existed between daily DMI and daily WI (r=0.63) as well as between cows’ daily BW and daily WI (r=0.23). The results warrant further investigations to determine whether monitoring of DMI, WI and BW may assist in predicting estrus.