The effects of dietary protein content and feeding level on the utilization of metabolizable energy (ME) and on the rates of gain, protein and fat deposition have been studied in seventy-two Iberian pigs growing from 15 to 50 kg body weight (BW) by means of comparative slaughter experiments. The animals were fed on six diets providing 223, 192, 175, 156, 129 and 101 g crude ideal protein (N £ 6·25; CP)/kg DM and 14·64, 14·14, 14·37, 14·80, 15·36 and 15·53 MJ ME/kg DM respectively. Each diet was offered at three levels of feeding: 0·60, 0·80 and 0·95 £ ad libitum intake. Protein deposition (PD) increased significantly (P,0·01) with each decrease in dietary CP content and reached a maximum value (74·0 g) when the diet providing 129 g CP/kg DM (6·86 g digestible ideal protein/MJ ME) was offered at the highest feeding level. This feeding regimen resulted in average values for live-weight gain and retained energy (RE) of 559 g/d and 10·9 MJ/d respectively. RE increased significantly (P, 0·001) from 480 to 626 kJ/kg BW 0·75 with each decrease in dietary CP content from 192 to 129 g/ kg DM. Raising the level of feed intake led to significant linear increases in PD and RE irrespective of the diet fed (P,0·001). When diets approaching an adequate supply of CP were given, the net efficiency of use of ME for growth (k w ) and the maintenance energy requirements were 58·2 % and 422 kJ/kg BW 0·75 per d respectively.

Nutritional requirements of the Iberian pig, a slow-growing, obese porcine breed, are not well defined and seem to differ from those of conventional or high-performing pigs. The effects of the dietary protein content and the feeding level on the utilisation of metabolisable energy (ME) and the rates of gain, protein, and fat deposition were studied with 81 Iberian castrates growing from 50 to 100 kg body weight (BW) by using the comparative slaughter technique. The animals were fed 4 diets providing 145, 120, 95, and 70 g ideal crude protein (CP) per kg dry matter (DM), and containing 13. 94, 14.29, 14.56, and 14.83 MJ ME per kg DM, respectively. Three levels of feeding were evaluated: 0.60, 0.80, and 0.95 £ ad libitum intake. Growth rate increased (linear and quadratic, P , 0.001) as the dietary ideal CP content decreased. It also increased with the feeding level (linear, P , 0.001; quadratic, P , 0.05). Gain:feed and gain:ME intake improved by decreasing the ideal CP content in the diet (linear, P , 0.001 and P , 0.05, respectively; quadratic P , 0.001 for both variables). Increasing the feeding level improved linearly gain:feed and gain:ME intake ( P , 0.001). Protein deposition (PD):ME intake ranged between 1.23 and 1.44 g/MJ, and it showed a tendency to reach the maximum value when the diet providing 95 g ideal CP per kg DM was fed (quadratic, P ¼ 0.078). When this diet was offered at 0.95 £ ad libitum, PD reached a maximum value of 71 g/day. This dietary treatment resulted in average values for average daily gain and retained energy (RE) of 854 g/day and 21.4 MJ/day, respectively. The average rate of gain was 19.93 g/MJ increase in ME intake, equivalent to an energy cost of 50.2 kJ ME per g gain, irrespective of the dietary ideal CP content. Also, the overall marginal efficiency of protein deposition (DPD:DME; g/MJ) was 1.34. Increasing the feeding level led to increases in PD (linear, P , 0.001) and RE (linear, P , 0.001; quadratic, P , 0.01) irrespective of the dietary ideal CP concentrations. Between 50 and 100 kg BW, the chemical composition of 1 kg gain averaged 78, 592, 28.7, and 284 g for CP, fat, ash, and water respectively. The net efficiency of use of ME for growth ( k g ) and the maintenance energy requirements were 0.606 and 396 kJ/kg BW 0.75 per day, respectively. The results support earlier findings that the genotype has marked effects on protein and energy metabolism of growing pigs and underline important compositional differences of the Iberian pig compared with conventional or modern porcine genotypes.

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Twelve goats of the Granadina breed in mid-and late lactation were used in two consecutive years to determine their protein and energy requirements for lactation. The animals were individually fed on diets based on pelleted lucerne (Medicago sativa) hay and barley. A total of six balance experiments were carried out. Gas exchange was measured using open-circuit respiration chambers. Milk yield ranged widely from 0.649 to 1.742 kg/d in the first year and from 0.222 to 1.989 kg/d in the second year, a steady decline in milk output being observed as lactation progressed. Milk composition remained rather constant during the midstage of lactation, with an average content (/kg milk) for total solids, total nitrogen, fat and gross energy of 149.7 g, 5.39 g, 58.8 g and 3.59 MJ respectively. Total endogenous N, endogenous urinary N and maintenance requirement for N in lactating goats were estimated to be 244, 218 mg N/kg body-weight (W)07' per d and 478 mg total N/kg W0" per d respectively from regression equations. A constant efficiency of use of dietary N for milk N plus retained N of 51.0% was found. By regressing milk energy plus apparent body energy retention or loss on metabolizable energy (ME) intake, the maintenance energy requirement was estimated to be 401 k J ME/kg Wo75 per d. When estimating the corrected milk yield as milk energy + (0.84 x negative energy retention) + (1.05 x positive energy retention), regression analysis indicated that the overall efficiency of use of M E for lactation was 66.7%. Also, from a plot of apparent body energy retention Y . milk energy yield, both expressed as a percentage of M E intake above maintenance, the efficiency with which ME was used to promote energy retention in the body during lactation was calculated to be 0.907 times that for milk secretion.Energy metabolism : Protein metabolism : Goats Although nutrient requirements are now relatively well-defined in sheep and cattle, there is still a lack of reliable information in the literature about the nutritional needs of lactating goats. Most available information has relied on extrapolations of values derived from cattle and sheep experiments. Nevertheless, because of the specific physiological features of the goat, this approach needs further validation. Previous reports on protein and energy requirements of lactating goats have been derived mainly from feeding trials and only a limited number of studies have published results on nitrogen and energy balance trials. N requirements for maintenance and milk production in lactating goats have been obtained by N balance studies by Khouri (1974), Sengar (1980, Rajpoot et al. (1981), Brun-Bellut et al. (1984) and Ciszuk & Lindberg (1985). These studies indicate that, in goats, the N requirements for maintenance might be in agreement with reported findings for dairy cattle and sheep and also that the efficiency of use of dietary N for milk-protein synthesis appears to be somewhat lower than values given for dairy cattle. To our knowledge, the work of Armstrong & Blaxter (1 965), ...