The effects of food protein content on the performance of pigs previously given foods with low or moderate protein contents

ABSTRACTAn experiment was conducted to study the ability of the pig to recover from the effects of a period on a food deficient in crude protein (CP). Forty young pigs were given free and continuous access to foods with either 150 (L) or 252 (M) g CP per kg in period 1 of the experiment, from 6·3 kg to 13·4 and 12·3 kg live weight respectively. These live weights were expected to give equal lipid-free empty body weights. In period 2, four males and four females from each of the period 1 treatments were given access to either M or a food with 377 g CP per kg (H) to a live weight of 30 kg, when the 32 pigs were killed.Pigs on L took 11 (s.e. 0·6) days longer to complete period 1, and had, at the end of this period, 0·20 (s.e. 0·03) kg less protein and 1·20 (s.e. 0·06) kg more lipid in their bodies than the M pigs, at a common ash weight. In period 2, pigs from L grew at a faster rate (750v.633 (s.e.d. 20) g/day), ate food at the same rate (1115v.1085 (s.e.d. 35) g/day) and converted food more efficiently (0·676v.0·585 (s.e.d. 0·016) g gain per g food) than those from M. At 30·3 kg live weight the pigs from L had corrected their protein deficit relative to ash and reduced their fatness, so that they had the same protein: ash ratio and only 0·47 (s.e. 0·12) kg more lipid in their bodies than those from M. This was the result of a higher rate of gain of protein and water, a lower rate of lipid gain and similar rate of ash gain by the pigs from L than those from M. In the first 7 days of period 2 the pigs from L gained weight at 1·4 times the rate of those from M. In the final 7 days there was no significant effect of period 1 treatment on growth rate. The pigs from L given food H in period 2 were more efficient than those given M in period 2 (food conversion efficiency (FCE) values of 0·884 and 0·791 respectively; s.e.d. 0·027), but this difference was reversed in the final 7 days (FCE values of 0·521 and 0·603 respectively). t I is concluded from these results that a period of eating a food of low protein content produces a reduced protein: ash and an increased lipid: ash ratio in the body and reduced growth rate and efficiency. When subsequently pigs are given a food of sufficiently high protein content, the protein: ash and lipid: ash ratios return to normal. The repletion of labile protein reserves, with their associated water, leads to a substantial increase in the rate of live-weight gain. The lower lipid content of the gain leads to a high efficiency. The duration of these effects depends on the protein content of the food given.</jats:p