Genome-wide association analyses based on a multiple-trait approach for modeling feed efficiency

Genome-wide association (GWA) of feed efficiency (FE) could help target important genomic regions influencing FE. Data provided by an international dairy FE research consortium consisted of phenotypic records on dry matter intakes (DMI), milk energy (MILKE), and metabolic body weight (MBW) on 6,937 cows from 16 stations in 4 counties. Of these cows, 4,916 had genotypes on 57,347 single nucleotide polymorphism (SNP) markers. We compared a GWA analysis based on the more classical residual feed intake (RFI) model with one based on a previously proposed multiple trait (MT) approach for modeling FE using an alternative measure (DMI|MILKE,MBW). Both models were based on a single-step genomic BLUP procedure that allowed the use of phenotypes from both genotyped and nongenotyped cows. Estimated effects for single SNP markers were small and not statistically important but virtually identical for either FE measure (RFI vs. DMI|MILKE,MBW). However, upon further refining this analysis to develop joint tests within nonoverlapping 1-Mb windows, significant associations were detected between either measure of FE with a window on each of Bos taurus autosomes BTA12 and BTA26. There was, as expected, no overlap between detected genomic regions for DMI|MILKE,MBW and genomic regions influencing the energy sink traits (i.e., MILKE and MBW) because of orthogonal relationships clearly defined between the various traits. Conversely, GWA inferences on DMI can be demonstrated to be partly driven by genetic associations between DMI with these same energy sink traits, thereby having clear implications when comparing GWA studies on DMI to GWA studies on FE-like measures such as RFI.

Modeling genetic and nongenetic variation of feed efficiency and its partial relationships between component traits as a function of management and environmental factors

Feed efficiency (FE), characterized as the fraction of feed nutrients converted into salable milk or meat, is of increasing economic importance in the dairy industry. We conjecture that FE is a complex trait whose variation and relationships or partial efficiencies (PE) involving the conversion of dry matter intake to milk energy and metabolic body weight may be highly heterogeneous across environments or management scenarios. In this study, a hierarchical Bayesian multivariate mixed model was proposed to jointly infer upon such heterogeneity at both genetic and nongenetic levels on PE and variance components (VC). The heterogeneity was modeled by embedding mixed effects specifications on PE and VC in addition to those directly specified on the component traits. We validated the model by simulation and applied it to a joint analysis of a dairy FE consortium data set with 5,088 Holstein cows from 13 research stations in Canada, the Netherlands, the United Kingdom, and the United States. Although no differences were detected among research stations for PE at the genetic level, some evidence was found of heterogeneity in residual PE. Furthermore, substantial heterogeneity in VC across stations, parities, and ration was observed with heritability estimates of FE ranging from 0.16 to 0.46 across stations.

Comparison of supplementation of n-3 fatty acids from fish and flax oil on cytokine gene expression and growth of milk-fed Holstein calves

The ability to reduce incidence of disease in calves and improve early vaccination strategies is of particular interest for dairy producers. The n-3 fatty acids have been reported to reduce inflammatory diseases in humans but limited research has been done in calves. The objective of this study was to compare supplementation of n-3 fatty acids from fish and flax oil on gene expression of whole blood cells and growth of milk-fed Holstein calves. Forty-eight Holstein bull calves from a commercial dairy were randomly assigned to 1 of 3 diets beginning at 4d old: (1) control milk replacer (MR) with all pork fat, (2) MR with 2% flax oil, and (3) MR with 2% fish oil. All MR were 17% fat, 27% crude protein on a dry matter (DM) basis, with all protein from whey sources. Calves were each fed 654g DM of MR daily for the first 25d and then 327g/d for d26, 27, and 28. On d28, calves were challenged with a Pasteurella vaccine and the temperature response to the vaccine was recorded. Milk and feed intake and fecal scores were recorded daily, and body weight and hip width were recorded weekly. Blood was collected from all calves on d25. One tube of collected blood was incubated with endotoxin (lipopolysaccharide; LPS) for 2h and frozen with a second tube of control blood. Quantitative real-time PCR was used to assess the effects of LPS stimulation on cytokine gene expression. During the 28 d, calves supplemented with flax oil had a greater growth rate and feed efficiency than calves fed fish oil (0.52±0.02 vs. 0.48±0.02g of gain:g of feed). Fish oil tended to decrease LPS stimulation of tumor necrosis factor-α expression. Flax oil, but not fish oil, decreased the expression of IL-4 and tended to decrease expression of osteopontin and IL-8. Flax oil tended to reduce the increase in rectal temperature in response to a Pasteurella vaccine. In conclusion, our data support the idea that supplementation with n-3 fatty acids affects cytokine gene expression.

Fatty acid intake alters growth and immunity in milk-fed calves

The aim of the present study was to determine the effect of supplementing milk replacer (MR) with NeoTec4 (Provimi North America, Brookville, OH), a commercially available blend of butyric acid, coconut oil, and flax oil, on calf growth, efficiency, and indices of immune function. In trial 1a, 48 male Holstein calves were fed either a control MR that contained only animal fat or the same MR with NeoTec4 (treatment) along with free-choice starter. The MR (28.7% crude protein, 15.6% fat) was fed at an average of 1 kg of dry matter (DM)/d. In trial 1b, weaned calves from trial 1a were all fed dry starter for 28 d without NeoTec4 (phase 1), and then half the calves were fed NeoTec4 for 28 d (phase 2). In trial 2, 40 male Holstein calves were fed a control MR with lard, coconut oil, and soy lecithin or the same MR supplemented with NeoTec4 (treatment). The MR (22.8% crude protein, 18.9% fat) was fed at an average of 1 kg of DM/d; no starter was fed. In trial 1a, NeoTec4 improved average daily gain, feed intake, and feed efficiency, reduced the number of days that calves experienced scours, and reduced the medical treatments for clostridium sickness. In trials 1a and 2, NeoTec4 altered the inflammatory response to vaccination with Pasteurella at 5 wk of age and to challenge with Salmonella toxin at less than 2 wk of age (fed NeoTec4 for 6 d), as observed by reduced hyperthermia and hypophagia, and altered the tumor necrosis factor-α response. In addition, NeoTec4 enhanced the response in IL-4 and globular protein estimates postchallenge and enhanced titers for bovine viral diarrhea and respiratory parainfluenza-3. Postchallenge serum concentrations of albumin were lower and urea nitrogen concentrations were greater in control calves than in calves fed NeoTec4. In trial 1b, performance did not differ during the first 28 d when no calves received NeoTec4, but calves receiving NeoTec4 in the second 28 d had greater average daily gain and feed efficiency. We conclude that supplementation of MR with NeoTec4 alters some immune and inflammatory responses, including increasing titers to bovine viral diarrhea and respiratory parainfluenza-3 vaccinations, reduces scours, reduces medical treatments for clostridium sickness, and improves growth rates and feed efficiency.

Short Communication: Intramammary Infusion of IGF-I Increases Bromodeoxyuridine Labeling in Mammary Epithelial Cells of Prepubertal Heifers

When dairy heifers are fed to gain more than 900 g of body weight/d, they have less mammary parenchymal DNA at puberty but more insulin-like growth factor-I (IGF-I) in serum. This negative relationship between serum IGF-I concentration and mammary epithelial cell proliferation is in disagreement with the extensively reported role of IGF-I as a stimulator of mammary epithelial cell proliferation. Despite the large body of evidence suggesting that an increase in IGF-I concentration should lead to an increase in mammary epithelial cell proliferation of prepubertal heifers, it had not been previously tested. Our objective was to determine if intramammary infusions of IGF-I would stimulate mammogenesis in prepubertal heifers in vivo. After 7 d of treatment, bromodeoxyuridine was infused intravenously and heifers were slaughtered 3 h later. Samples from 3 regions of the mammary parenchyma were collected, fixed, sliced, and incubated with bromodeoxyuridine monoclonal antibody to identify cells in the S-phase of the cell cycle. Intramammary infusion of IGF-I increased the percentage of epithelial cells in the S-phase by 52% (6.4 vs. 4.2%, +/- 0.3%). Proliferation was similar in all 3 parenchymal regions, and the response to IGF-I was similar in each region. We conclude that local IGF-I increases proliferation of mammary parenchymal epithelial cells in prepubertal heifers.

Effect of increasing energy and protein intake on mammary development in heifer calves

The objective of this study was to determine if increased energy and protein intake from 2 to 14 wk of age would affect mammary development in heifer calves. At 2 wk of age, Holstein heifer calves were assigned to 1 of 4 treatments in a 2 x 2 factorial arrangement with 2 levels of protein and energy intake (moderate, M; high, H) in period 1 (2 to 8 wk of age) and 2 levels of protein and energy intake (low, L; high, H) in period 2 (8 to 14 wk of age), so that mean initial body weights were approximately equal for all 4 treatments (ML, MH, HL, and HH). The M diet in period 1 consisted of a standard milk replacer (21.3% CP, 21.3% fat) fed at 1.1% of BW on a DM basis and a 16.5% CP grain mix fed at restricted intake to promote 400 g of daily gain, whereas the L diet in period 2 consisted only of the grain mix. The H diet in period 1 consisted of a high-protein milk replacer (30.3% CP, 15.9% fat) fed at 2.0% of body weight on a DM basis and a 21.3% CP grain mix available ad libitum. In period 2, the H diet consisted of just the 21.3% grain mix. Calves were gradually weaned from milk replacer by 7 wk and slaughtered at 8 (n = 11) or 14 wk of age (n = 41). Parenchyma from the distal region, midgland, and proximal region relative to the teat from one half of the udder was collected, fixed, and embedded in paraffin. The other half of the gland was used to determine parenchymal mass, protein, fat, DNA, RNA, and extraparenchymal mass. Total parenchymal tissue, parenchymal DNA, parenchymal RNA, and concentrations of DNA and RNA were higher for calves on the H diet during period 1, but were not affected by diet during period 2. Parenchymal fat percentage was increased by the H diet during period 2. The H diet increased extraparenchymal fat during both periods. The area of parenchyma occupied by epithelium was not affected by treatment, but at the end of period 2, the percentage of proliferating epithelial cells as indicated by Ki67, an marker of cell proliferation, expression was greater for calves on the M diet in period 1 compared with calves on the H diet in period 1. Diets did not influence parenchymal protein percentage or the ratio of RNA to DNA. Higher energy and protein intake from 2 to 8 wk of age increased parenchymal mass and parenchymal DNA and RNA in mammary glands of heifer calves without increasing deposition of parenchymal fat. Diet also influenced histological development of mammary parenchyma and subsequent proliferation of ductal epithelial cells. Implications of these effects for future milk production potential are unknown.

Effect of increasing energy and protein intake on body growth and carcass composition of heifer calves

The objective was to determine whether increased energy and protein intake between 2 and 14 wk of age would increase growth rates of heifer calves without fattening. At 2 wk of age, Holstein heifer calves were assigned to 1 of 4 treatments in a 2 x 2 factorial arrangement with 2 levels of protein and energy intake (moderate [M]; high [H]) in period 1 (2 to 8 wk of age) by 2 levels of protein and energy intake (low [L]; high [H]) in period 2 (8 to 14 wk of age) to produce similar initial BW for all 4 treatments. Treatments were ML, MH, HL, and HH, indicating moderate or high energy and protein intake during the first period and low or high intake during the second period. The M diet consisted of a standard milk replacer (21.3% CP, 21.3% fat) fed at 1.1% of BW on a DM basis and a 16.5% CP grain mix fed at restricted intake to promote 400 g of average daily gain (ADG), whereas the L diet consisted only of the grain mix. The H diet consisted of a high-protein milk replacer (30.3% CP, 15.9% fat) fed at 2% of BW on a DM basis and a 21.3% CP grain mix available ad libitum. Calves were weaned gradually from milk replacer by 7 wk and slaughtered at 8 (n = 11) or 14 wk of age (n = 41). In periods 1 and 2, ADG and the gain:feed ratio were greater for calves fed the H diet. Calves fed the H diet were taller after both periods 1 and 2. No difference was observed in carcass composition at 8 wk, but at 14 wk calves fed MH and HH had less water and more fat than calves fed ML and HL. Plasma IGF-I concentrations were greatest for calves fed the H diet during either period. Plasma leptin concentrations were increased in calves fed the H diet during period 1 from 4 to 6 wk of age. Increasing energy and protein intake from 2 to 8 wk and 8 to 14 wk of age increased BW, withers height, and gain:feed ratio. Calves fed the H diet from 8 to 14 wk of age had more body fat than calves fed the L diet. Increased energy and protein intake can increase the rate of body growth of heifer calves and potentially reduce rearing costs.

Effects of diet and injection of bovine somatotropin on prepubertal growth and first-lactation milk yields of Holstein cows

To determine effects of rapid prepubertal growth on first-lactation milk production, Holstein heifers were randomly assigned to one of three treatments. Thirty-five heifers were fed a standard diet to meet NRC recommendations and produce 0.8 kg of body weight (BW) gain/d (standard). Thirty-five heifers were fed a diet with higher energy (2.8 Mcal of metabolizable energy/kg) and protein (19.7% crude protein; high diet) to produce 1.2 kg of BW gain/d (high). Thirty-five heifers were fed the high diet and injected daily with bovine somatotropin (bST) (25 microg/kg of BW; high-bST). Diets were fed and bST was injected from 135 kg of BW until pregnancy was confirmed. Heifers were inseminated after BW exceeded 363 kg. Pregnant heifers were commingled and fed similar diets through gestation, parturition, and lactation. High and high-bST heifers had greater prebreeding average BW gains than standard heifers. Conversely, standard heifers had a greater average BW gain during gestation than high and high-bST heifers. High and high-bST heifers were approximately 90 d younger than standard heifers at first insemination and first parturition. Postpartum BW, body condition scores, and withers heights at parturition, and calving ease scores were not different among treatments. Standard heifers produced 14% more milk than high heifers but not more than high-bST heifers. The high-protein, high-energy diet decreased age at first parturition and first-lactation milk production, but did not affect reproduction. Injection of bST during the prepubertal growth period combined with the high diet decreased age at first parturition without reducing milk production.

Expression of growth hormone receptor 1A messenger ribonucleic acid in liver of dairy cows during lactation and after administration of recombinant bovine somatotropin

The mRNA for growth hormone receptor is transcribed from at least three different promoters in cattle. The first promoter (P1) is liver-specific and transcribes growth hormone receptor mRNA containing exon 1A (growth hormone receptor 1A). The second and third promoters (P2 and P3) are active in a variety of tissues and transcribe growth hormone receptor mRNA containing exon 1B and 1C. The objective was to characterize P1 activity by measuring the amount of growth hormone receptor 1A mRNA in liver of dairy cows at different stages of lactation as well as after administration of recombinant bovine somatotropin (rbST). In study 1, liver RNA was isolated from Holstein cows during the dry period (nonlactating, n = 6) and during early (n = 6), mid (n = 6), and late (n = 11) stages of lactation. Six of the late-lactation cows received injections of rbST (25 mg/d) for 7 d prior to collection of liver tissue. In study 2, lactating Holstein cows received either no infusion (control, n = 10) or continuous infusion of rbST (29 mg/d, n = 10) for 63 d. The amount of growth hormone receptor 1A mRNA was decreased in early- and mid-lactation cows compared with late-lactation cows or nonlactating cows (study 1). Administration of rbST increased growth hormone receptor 1A mRNA (studies 1 and 2). The total amount of growth hormone receptor transcribed from alternative promoters (growth hormone receptor P2 and P3) remained unchanged during different stages of lactation or in response to rbST. We conclude that changes in liver growth hormone receptor mRNA in lactating dairy cattle primarily depend on growth hormone receptor P1 activity.

Effect of energy and protein density of prepartum diets on fat and protein metabolism of dairy cattle in the periparturient period

To determine if increased nutrient density in prepartum diets improves nutrient balance of peripartum cows, we blocked 40 Holstein cows and 40 heifers by expected date of parturition and assigned them randomly within blocks to one of four treatment diets varying in density of net energy for lactation (NEL) and crude protein (CP). Diets were 1.30 Mcal of NEL/kg and 12.2% CP, 1.49 Mcal of NEL/kg and 14.2% CP, 1.61 Mcal of NEL/kg and 15.9% CP, and 1.48 Mcal of NEL/kg and 16.2% CP. These diets were fed ad libitum from 25 d prepartum until parturition, and all cows were fed the same diet after calving. Increased nutrient-density of prepartum diets did not decrease feed intake. Compared to animals fed the lowest density, those fed the highest density consumed more NEL (20 vs. 14 Mcal/d) and gained more body condition, backfat, and body weight. They also had less nonesterified fatty acids in plasma (176 vs. 233 microM) and more insulin-like growth factor-I in plasma (472 vs. 390 ng/ml) during the last 2 wk prepartum and less triglyceride in liver at parturition (0.9 vs. 1.5%, wet tissue basis). Quadratic effects of energy density were not observed, and the addition of protein in the medium energy diet had no effect. Prepartum diets did not alter any variables during lactation. In conclusion, increasing the energy and protein density up to 1.6 Mcal of NEL/kg and 16% CP in diets during the last month before parturition improves nutrient balance of cattle prepartum and decreases hepatic lipid content at parturition.

Dry cow diet, management, and energy balance as risk factors for displaced abomasum in high producing dairy herds

The objective of this study was to determine prepartum risk factors for displaced abomasum. The design was a prospective study of 1170 multiparous Holstein cows from 67 high producing dairy herds in Michigan. Each farm was visited four times within a 6-wk period. At each visit, data on nutrition and management were collected. All multiparous cows within 35 d of projected calving were assigned a body condition score, and blood was sampled to determine the concentration of nonesterified fatty acids in plasma. A multivariable linear regression model was used to determine risk factors associated with the incidence of displaced abomasum during lactation on a herd basis. A multivariable logistic regression model with random effect was used to determine risk factors for displaced abomasum on an individual cow basis. Significant risk factors for displaced abomasum included a negative energy balance prepartum (as estimated from plasma nonesterified fatty acids), a high body condition score, suboptimal feed bunk management prepartum, prepartum diets containing > 1.65 Mcal of net energy for lactation/kg of dry matter, winter and summer seasons, high genetic merit, and low parity.

Efficiency of nutrient use and relationship to profitability on dairy farms

As cows eat more feed to support higher milk production, the proportion of digested energy that is captured in milk increases. In contrast, as cows consume more feed, digestive efficiency decreases, but the magnitude of depression in digestibility is not characterized for high producing cows. Despite the digestibility depression, biological efficiency increases considerably as Holstein cows produce more milk up to 15,000 kg/yr. Above 15,000 kg/yr, the gain in biological efficiency per unit of increase in milk production is expected to approach 0. At 21,000 kg of milk/yr, approximately 25% of the gross energy consumed by the cow during the first 5 yr of life likely would be captured as milk, conceptus, or body tissues; further gains in biological efficiency are not likely without major advances in feed digestion. Although feeds generally cost more as cows are fed for higher milk production, increased productivity also enhances profitability, partly because of increased efficiency but also because fixed costs are decreased relative to total costs. This relationship between productivity and profitability is expected to continue up to > 21,000 kg/yr per cow. Other issues related to the efficiency of nutrient use will become more important in the future, namely, efficiency of the use of feeds that can also be consumed by humans, efficiency of use of tillable land, and minimization of nutrient losses to the environment.

Comparison of growth hormone-releasing factor and somatotropin: body growth and lactation of primiparous cows

Growth hormone-releasing factor is the main endogenous stimulator of somatotropin secretion. Our objective was to compare the effects of recombinant growth hormone-releasing factor and recombinant bST on somatotropin secretion, mammary function, and body composition of lactating, primiparous dairy cows. Cows (118 d of lactation) served as uninfused controls or were infused for 63 d with 12 mg/d of releasing factor or with 29 mg/d of bST. These doses elevated somatotropin in serum to concentrations of similar magnitude. The releasing factor and bST each similarly increased milk yield, yield of milk components, weight of most organs, mobilization of adipose tissue, accretion of lean tissue in the carcass, and metabolic activity (RNA) of mammary tissue. Relative to controls, neither releasing factor nor bST significantly affected cell numbers (DNA) in mammary glands or concentrations of plasmin in milk. None of the variables measured provided evidence for galactopoietic effects of releasing factor independent of somatotropin.

Comparison of growth hormone-releasing factor and somatotropin: the somatotropic axis in lactating primiparous cows

Our objective was to compare the effects of recombinant bovine growth hormone-releasing factor and recombinant bST on the somatotropic cascade in lactating dairy cows. Primiparous cows were killed after 63 d of continuous daily infusion with 12 mg of releasing factor or 29 mg of bST or no infusion (controls). Both hormone infusions similarly increased mean concentration of somatotropin in serum, but pulsatility of somatotropin in serum was greater for cows given releasing factor. Both hormone infusions increased the amounts of IGF-I in serum, IGF-I mRNA in liver, and IGF-binding protein-3 in serum and decreased IGF binding protein-2 in serum, but these effects were less for cows given releasing factor than for those given bST. Both infusions decreased the number of free binding sites for IGF-I in mammary tissue. In liver, treatment did not alter the abundance of mRNA for the somatotropin receptor or the number of free binding sites for somatotropin. Results suggest that endogenous somatotropin is less effective as an IGF-I secretagogue than is exogenous bST infused continuously, yet the releasing factor and bST increased milk yield similarly. We conclude that growth hormone-releasing factor stimulates milk synthesis mostly through the same mechanisms as bST, but that serum IGF-I alone is not a good indicator of the galactopoietic potency of the two hormones.

Effect of dietary energy restriction on the expression of insulin-like growth factor-I in liver and corpus luteum of heifers

The effects of energy balance on the corpus luteum may be mediated by IGF-I. Our objective was to determine whether negative energy balance decreases expression of IGF-I mRNA in the liver or corpus luteum of heifers. For four consecutive estrous cycles, 14 Holstein heifers were maintained in negative or positive energy balance to lose 510 g/d of BW or gain 560 g/d of BW, respectively. The liver was biopsied and the corpus luteum was collected 7 d after fourth estrus. Heifers fed below maintenance had a smaller corpus luteum than did control heifers. Compared with that of controls, negative energy balance increased growth hormone in serum but decreased IGF-I in serum and the abundance of mRNA for growth hormone receptor and IGF-I in liver. In contrast, diet did not affect the abundance of mRNA for the growth hormone receptor or IGF-I in luteal tissue. Negative energy balance increased IGF binding protein-2 in serum but did not affect IGF binding protein-3. We conclude that negative energy balance of cattle decreases IGF-I mRNA abundance in the liver but not in the 7-d corpus luteum. If decreased IGF-I mediates the adverse effect of negative energy balance on luteal growth, the mode of action is likely endocrine, not autocrine or paracrine.

Expression of insulin-like growth factor-I in cows at different stages of lactation and in late lactation cows treated with somatotropin

Relative amounts of IGF-I mRNA were measured in livers of Holstein cows at different stages of lactation (6 early, 6 mid, 6 late lactation, 6 dry) and 6 late lactation cows treated with bST for 1 wk. Milk yield was greater for early lactation cows than for mid and late lactation controls. All cows except those in early lactation were in positive energy balance. Serum IGF-I increased as lactation progressed and was greatest during the dry period. Liver IGF-I mRNA was less in cows in early than in late lactation but greater in lactating than in dry cows. Treatment with bST increased milk yield and concentrations of serum IGF-I, hepatic IGF-I mRNA, and serum IGF-binding protein-3, decreased concentration of serum IGF-binding protein-2, and did not alter abundance of mammary IGF-I mRNA. These parallel changes in serum IGF-I and hepatic IGF-I mRNA suggest that exogenous bST increases IGF-I synthesis in liver of cows during late lactation and that IGF-I synthesis is depressed during early lactation when cows are in negative energy balance. We conclude that IGF-I may play an endocrine role in mediating galactopoietic effects of exogenous bST during late lactation. However, the role of IGF-I during early lactation remains unclear.

Protein and fat metabolism in cows given somavubove before parturition

Forty-one Holstein cows were injected with 0, 5, or 14 mg/d of bST for the last 46 +/- 6 d before parturition. Compared with data for controls, the 5- and 14-mg doses of bST increased apparent protein synthesis about 16% before parturition. Exogenous bST before parturition increased apparent protein degradation 30% during wk 1 after parturition. During wk 1 of lactation, 14 mg of bST also increased milk protein yield 33%. No treatment differences were present in concentration of serum NEFA, body condition score, or thickness of subcutaneous fat. Therefore, administration of bST before parturition did not alter metabolism of subcutaneous fat. Prepartum treatment with 5 and 14 mg of bST increased and maintained serum somatotropin at 6.5 and 22.7 ng/ml, respectively, compared with 1.6 ng/ml in controls. Concentrations of serum IGF-I were initially increased but were not maintained as parturition approached. On d -23, IGF binding protein 3 was increased 65% but was not different among groups by d -7. For groups administered the 5 and 14 mg/d of bST, IGF binding protein 2 was decreased 40%. Administration of bST before parturition increased protein reserves and stimulated milk protein yield for 1 wk but did not alter metabolism of subcutaneous fat. Furthermore, energy balance appeared to be a major regulator of concentrations of IGF binding protein 3 and responsiveness of IGF-I to exogenous somatotropin before parturition.

Milk production and composition in cows and goats fed alpha-ketoisocaproate

To examine whether alpha-ketoisocaproate supplementation affects milk production, 10 goats were fed either 0 or 1.1% calcium-alpha-ketoisocaproate for 2 wk and 12 cows were fed either 0 or .75% Na alpha-ketoisocaproate for 3 wk. Supplementation with alpha-ketoisocaproate increased milk fat content, milk fat yield, and 4% FCM yield in cows by an average of 5, 10, and 8%, respectively, for the treatment period. In cows, response of milk fat yield to alpha-ketoisocaproate was 120 g during wk 1 of treatment but diminished to 55 g by wk 3. Milk yield and milk protein yield tended to be greater in cows fed alpha-ketoisocaproate, but milk production efficiency and body weight were not altered by treatment in either species. Supplementation with alpha-ketoisocaproate had no significant effect on fatty acid composition of milk but tended to increase the percentage of C10 and C12 fatty acids. In goats, supplementation with alpha-ketoisocaproate had no significant effect on milk production or composition, but trends toward increased milk fat and protein content were observed. Results indicate that alpha-ketoisocaproate acutely stimulates milk fat production in lactating cows and that this effect seems to diminish with time.

Effects of dietary leucine, alpha-ketoisocaproate and isovalerate on antibody production and lymphocyte blastogenesis in growing lambs

The chronic effects of oral leucine and leucine metabolites on sheep immune function were determined in two experiments. In replicate experiments, 30 mixed-breed ram lambs were individually fed diets supplemented with approximately 0.05% ruminally protected limestone (control), alpha-ketoisocaproate (KIC), isovalerate (IVA) or leucine (Leu). Serum titers of antibodies produced in response to Brucella abortus antigen and porcine red blood cells were determined. Mitogen-stimulated lymphocyte blastogenesis was determined in experiment 2 by adding phytohemagglutinin (PHA), concanavalin A (Con A) or pokeweed mitogen (PWM) to isolated lymphocytes and measuring [3H]thymidine incorporation. In both experiments, in lambs fed Leu, antibody production to porcine red blood cells was approximately 80% (P less than 0.05) of that in control animals. When KIC was fed, antibody titers to porcine red blood cells were approximately 120% (P less than 0.05) of that of controls. Compared to controls background lymphocyte blastogenesis was higher when KIC was fed, whereas background blastogenesis was lower when Leu was fed (KIC vs. Leu; P less than 0.05). IVA did not significantly affect either measurement. These data indicate that feeding Leu may adversely affect immune function by suppressing lymphocyte activity, whereas oral administration of KIC has a positive influence on immune function in sheep by increasing lymphocyte activity.