Effect of growth rate on mineral retention and body composition of growing lambs

Body chemical composition and efficiency of energy and nutrient utilization by growing pre-ruminant Saanen goat kids

An experiment involving a feeding trial and a comparative slaughter was conducted to assess the body chemical composition and patterns of nutrient utilization in pre-ruminant Saanen goat kids. Thirty male kids weighing about 6 kg were divided into five equal groups, one of which was slaughtered as the reference group (G0). The remainder were randomly assigned to four feeding levels of 250, 290, 330 and 370 g goats’ milk per kg M0·75 per day and named as groups GI, GII, GIII and GIV, respectively up to about 15 kg live weight, after which they were slaughtered. Mean milk consumption per unit live-weight gain (LWG) (kg/kg), and daily LWG (g/day), for GI, GII, GIII, GIV respectively were: 13·5 and 110; 10·5 and 160; 10·2 and 180; and 10·3 and 200. Empty body weight (EBW) as a proportion of final live weight was 0·95 in the reference animals, and ranged from 0·80 to 0·88 in the treatment groups. The dry matter (DM) concentration in the empty body of kids increased as their age advanced, from 277 g/kg EBW (G0) to between 308 and 326 g/kg EBW (GI to GIV). The protein and fat concentration of LWGs increased with the level of feeding from GI (142 g crude protein (CP) and 75·5 g fat per kg LWG) to GIV (155 g CP and 109 g fat per kg LWG). Regression of energy retention (ER) on metabolizable energy (ME) intake resulted in an efficiency of ME utilization for body retention (k) of 0·72(± 006). ME requirement for maintenance was estimated as 458 kJ/kg M0·75 per day. Efficiency of nitrogen (N) utilization for growth and N requirement for maintenance were estimated as 0·66(±011) and 0·47 g/kg M0·75 per day, respectively.

The effect of a change in blood acid-base status on body composition and mineral retention in growing lambs

Three groups of lambs of about 25 kg live weight were given a concentrate diet either on its own (eight lambs) or supplemented with 10 g/kg ammonium chloride (eight lambs) or 20 g/kg sodium bicarbonate (12 lambs). At about 45 kg live weight the lambs were killed and their body composition was determined. The composition of their gains was also determined using information obtained from a fourth group of lambs (eight lambs) which were killed at the start of the experiment. Lambs given the ammonium chloride diet showed a reduction in blood pH while those given the sodium bicarbonate diet showed an increase to levels seen in lambs given forage diets. There were also marked effects on calcium (Ca), phosphorus (P) and magnesium retention with retentions being reduced in those given the ammonium chloride diet and increased in those given the bicarbonate diet. The average rates of retention of Ca and P in lambs given the bicarbonate diet were 9·1 and 5·9 g/kg empty-body weight gain and are comparable with rates seen in lambs given forage diets. These results suggest that dietary induced changes in blood acid-base status is a major factor contributing to the lower rates of retentions of these minerals in lambs given cereal-based diets.

The dietary requirements of calcium and phosphorus for growing lambs

Groups of wether lambs were fed on four concentrate diets, from a live weight (LW) of about 25 kg until they had grown to about 50 kg, when they were killed, minced and analysed. A fifth group was killed at the start of the trial to provide data on their initial composition. The dietary treatments were identical except in their concentrations of calcium (Ca) and phosphorus (P) and supplied, with some approximations: (A) 0·75 times the requirements for Ca and P estimated according to the recommendations of the AFRC Technical Committee on Responses to Nutrients (TCORN, 1990); (B) a close match to the estimated requirements for both elements; (C) 1·5 times the estimated requirements for both elements; (D) 1·5 times the Ca requirement and 0·75 times the P requirement.

The retentions of Ca and P in the lambs were closely similar with diets B and C (6·8 and 7·3 g Ca per kg LW and 4·1 and 4·5 g P per kg LW) and significantly lower with diet A (4·8 g Ca and 3·0 g P per kg LW) and diet D (5·0 g Ca and 2·7 g P per kg LW). Parallel differences in response to diet were evident in the composition of the metacarpi. Plasma Ca and P concentrations showed no significant differences between the dietary treatments A, B and C, but plasma P concentrations were markedly depressed with lambs on diet D and plasma Ca concentrations were elevated in this group. Rumen P concentrations were also markedly lower in lambs on diet D and their food intakes and growth rates were lower than in lambs in other groups. The results indicate that Ca and P retentions were not increased by feeding these elements in excess of their estimated requirements and were reduced when Ca and P or P alone was reduced proportionately to about 0·75 times requirement. The data are in accord with the TCORN recommendations and suggests that they provide a satisfactory basis for defining Ca and P requirements for growing lambs.