Effect in sheep of dietary concentrate content on secretion of growth hormone, insulin and insulin-like growth factor-I after feeding

Effects of forage feeding on rumen fermentation, plasma metabolites, and hormones in Holstein calves during pre- and postweaning periods1

Recent studies have suggested that the amount of forage intake by calves around the time of weaning could affect ruminal pH levels. Several studies have also proposed that subacute ruminal acidosis in mature cows is a risk factor for various metabolic disorders and production diseases. In this study, we examined the effects of forage feeding on ruminal pH, ruminal fermentation, rumen lipopolysaccharide (LPS) concentration, plasma metabolites, and hormonal concentrations in calves during pre- and postweaning periods. Sixteen male Holstein calves were used. At 7 wk of age, calves were randomly assigned to one of two dietary treatments: calves in the HAY group (n = 8) were fed starter with forage, and those in the CON group (n = 8) were fed starter without any forage. All calves were weaned at 8 wk of age. The amounts of starter and mixed hay were gradually increased until the end of the experiment (age, 11 wk). Ruminal pH was measured continuously every 10 min using an indwelling sensor. Rumen fluid and peripheral blood samples were obtained prior to morning feedings at -1, 0, 1, and 3 wk after weaning. Compared with the HAY group, in the CON group, the average daily ruminal pH was lower (P < 0.05) and the duration of ruminal pH values below 5.6 was longer (P < 0.05). Regarding ruminal VFA profiles, compared with the HAY group, the CON group had lower (P < 0.05) acetate to propionate ratios at 1 and 3 wk after weaning. Rumen LPS concentrations tended to be higher (P < 0.1) in the CON group than in the HAY group; however, concentrations of LPS-binding protein, haptoglobin, and serum amyloid A in the peripheral blood did not differ significantly. Plasma aspartate aminotransferase and alkaline phosphatase levels were markedly higher (P < 0.05) in the CON group than in the HAY group at 1 and 3 wk after weaning. There was a linear decrease in plasma growth hormone (GH) levels in the CON group after the start of the experiment, and its concentrations were lower (P < 0.05) in the CON group than in the HAY group at 0 and 3 wk after weaning. The results indicated that forage provision during pre- and postweaning periods helped prevent decrease in ruminal pH, change in ruminal fermentation, and liver alteration, and helped maintain plasma GH levels, which suggests that calves around the time of weaning need forage intake with starter to maintain proper metabolic and hormonal functions.

Association of plasma metabolites and hormones with the growth and composition of lambs as affected by nutrition and sire genetics

An experiment was conducted to test 3 hypotheses regarding the variation in plasma parameters and their association with lamb growth and composition. The experiment tested whether sire genetics and available nutrition affected specific plasma traits, whether these traits were associated with growth and compositional characteristics, and whether data on plasma traits could improve the prediction of growth and carcass composition. Lambs (n = 103) produced by sires differing in estimated breeding values for growth, muscling, and fat were reared on LOW or HIGH planes of lifetime nutrition. Blood samples were collected immediately prior to weaning and before slaughter at 8 months of age. Concentrations of plasma creatinine (CRE), urea (PUN), insulin like growth factor I (IGF-I) were measured in all samples. Leptin was measured in samples from male lambs only (n = 56). HIGH nutrition increased preweaning and preslaughter IGF-I and leptin concentrations; nutritional effects on PUN and CRE were inconsistent. Lambs of the high muscle sire-type exhibited increased plasma IGF-I, reduced PUN, and an increased PUN : CRE ratio preweaning. Increased genetic potential of the sire for growth reduced PUN and increased PUN : CRE ratio. Plasma IGF-I correlated strongly with lamb growth rate (r2 = 0.49). Interaction of nutrition and sire-type for preslaughter leptin mimicked the interaction occurring for carcass fat, providing an example of selection on genotype inducing a physiological (hormonal) change and resulting in a modified phenotype. Stepwise regressions developed to predict carcass protein and fat mass from information available at weaning or at slaughter indicated that inclusion of plasma parameters in these models caused only small increases in the proportion of variance accounted for. The most significant benefit was an increase in the proportion of variance in carcass weight accounted for (from 65 to 73%) by including IGF-I and CRE as predictors compared with prediction from weaning weight alone. If slaughter data were available, then >90% of the variance in carcass fat and protein masses was explained by carcass weight alone and this was not increased by inclusion of any preslaughter plasma parameter in the model. It was concluded that while nutrition and the genetic capacity of the sire (especially for muscling) affect plasma constituents as well as lamb growth and carcass composition, the inclusion of the measured plasma traits in models to predict final carcass composition from weaning data or slaughter data is unlikely to improve the prediction sufficient to justify the additional measurement cost.