Protein, acetate and propionate for roughage-fed lambs. 2. Nutrient kinetics

Effects of dietary calcium propionate on growth performance and carcass characteristics of finishing lambs

The objective of this study was to evaluate the effects of the addition of two levels of calcium propionate on lamb performance and some carcass characteristics. Twenty-one male Creole lambs with an initial weight of 25.3 ± 3.3 kg were randomly assigned to one of the following treatments: 0, 10, and 20 g of calcium propionate/kg of diet (dry matter basis). Intake, daily gain, feed conversion, carcass weight, and rib eye area were not affected (P < 0.05) by calcium propionate addition. Ruminal fermentation was not altered (rumen pH, volatile fatty acids concentration, and fermentation pattern), and ruminal ammonia-N presented a quadratic response (P < 0.05). In fat from the longissimus dorsi muscle, oleic acid showed a linear decrease (P < 0.05) and α-linolenic presented a linear increment (P < 0.05). The addition of 10 or 20 g of calcium propionate in diets containing 350 g/kg grain and 100 g/kg molasses did not modify the productive performance of lambs or ruminal fermentation, and minor changes were detected in long-chain fatty acid in intramuscular fat.

Protein, acetate and propionate for roughage-fed lambs. 1. Body and blood composition

Sixty castrated male lambs fca. 37 kg) were allocated to an initial slaughter group (no. = 12) or to one of six treatment groups (no. = 8). Chopped oaten hay (sprayed with 10 g urea per kg) was offered ad libitum with 57 gjday chopped lucerne hay. Additional supplements were 0 or 57 g/day formaldehyde-treated casein (protected casein) and volatile fatty acids (VFAs) at ca. 1·45 MJ gross energy per day. The VFAs given were acetate or propionate or a mixture of these (molar ratio 4: 1). Daily food intake and weekly live-weight (LW) gain were measured and rumen fluid and blood were collected. The lambs were shorn, slaughtered and body composition was determined.

Food intake (g/kg LW) was not affected by treatments. Supplementation with protected casein increased LW gain and wool growth. Supplementation with propionate reduced LW gain, but not when given with protected casein. Plasma concentrations of urea-nitrogen and insulin were increased, and plasma somatotropin decreased in lambs given protected casein. Final body content of water, fat, protein and gross energy, adjusted to the mean fleece/digesta-free body weight of 36·5 kg, was not affected by the treatments. The partitioning of water, fat and energy between the carcass and the rest of the body was affected by the treatments. Excretion of VFAs in urine was measured in two sheep in experiment 2, and was negligible compared with the quantity of VFAs given. It is concluded that energy from salts of VFAs, in particular propionate, is used inefficiently for body-weight gain in lambs given low-protein roughage diets. The nutritional treatments had only marginal effects on the composition of body gain.

Responses of whole body protein synthesis, nitrogen retention and glucose kinetics to supplemental starch in goats

An isotope dilution experiment was conducted to determine the effect of metabolizable energy intake (MEI) as starch on whole body protein synthesis (WBPS), nitrogen (N) retention and glucose irreversible loss rate (ILR) in four adult goats (Capra hircus). The goats were fed isonitrogenous diets containing three different metabolizable energy (1.0, 1.5 and 2.0 times maintenance) twice daily. Energy above maintenance was supplemented with cornstarch. The WBPS and glucose ILR during 5 to 7 h after feeding were measured by a primed-continuous infusion of [2H5]phenylalanine, [2H2]tyrosine, [2H4]tyrosine and [13C6]glucose for 4 h, with measurements of plasma concentrations of metabolites and insulin. Ruminal characteristics were also determined. Increasing MEI improved N retention, despite decreased digestible N. Increasing MEI decreased ruminal pH and ammonia nitrogen. In plasma, decreased urea N, increased total amino N and tyrosine, and trends for increases in phenylalanine and insulin resulted from increasing MEI. Increasing MEI increased ILR of glucose, phenylalanine and tyrosine, and hydroxylation rate of phenylalanine and WBPS. We conclude that in goats increasing MEI as starch enhances WBPS in the absorptive state and N retention, despite a decrease in digestible N. These changes are probably associated with both decreased ammonia absorption and increased amino acid absorption.