THE EFFECT OF EXOGENOUS PROLACTIN ON LACTATION PERFORMANCE OF FIRST-LITTER SOWS GIVEN PROTEIN-DEFICIENT DIETS DURING THE FIRST PREGNANCY

Twenty-four sows were used to study the effects of dietary protein res triction during pregnancy and exogenous porcine prolactin (pPRL) durin g late pregnancy and throughout lactation on lactation performance, Ei ght sows were given a protein-adequate diet containing 179 g crude pro tein (CP) kg(-1) during their first pregnancy while the remaining 16 s ows received the same amount of a diet containing 80 g CP kg(-1). Eigh t of the sows given 80 g CP kg(-1) during pregnancy were injected with 15 mg pPRL i.m. twice daily at 08:00 and 20:00 between day (d) 102.1 (+/-0.3) of pregnancy and weaning after their first lactation. Pregnan t sows offered the low protein diet gained significantly less body wei ght during gestation and tended to eat less in the subsequent lactatio n than sows given the protein-adequate diet. Dietary protein had no si gnificant effect on birth weight, milk yield, milk composition or grow th rate of the litter during lactation. Neither dietary protein intake during pregnancy nor exogenous prolactin affected the concentrations of plasma glucose, serum insulin, urea or non-esterified fatty acid (N EFA) during lactation. The concentration of lactose in plasma during l actation was unaffected by treatment, but at d 105 of pregnancy, plasm a lactose levels were greater in sows which bad received exogenous pro lactin (32.4 vs. 6.2 mg l(-1), P < 0.05). The concentrations of RNA an d DNA in mammary tissue biopsies were unaffected by either dietary pro tein or pPRL. The concentration of RNA and DNA increased between d 70 and 90 from 0.66 to 2.77 mg g(-1) and from 0.54 to 1.19 mg g(-1), resp ectively. Thereafter, RNA increased to 4.40 mg g(-1) at d 14 of lactat ion whilst DNA concentration remained at a similar level of 0.90 mg g( -1). Milk yield of sows between d 5 and 8 and between d 19 and 22 of l actation was reduced from 8.36 to 7.00 kg day(-1) and from 10.74 to 8. 22 kg day(-1), respectively, in sows given pPRL. The protein content o f colostrum from sows treated with pPRL was reduced from 164 to 104 g kg(-1) whereas the fat content increased from 47 to 127 g kg(-1). Thes e results indicate that the administration of exogenous pPRL during la te pregnancy and throughout lactation initiated lactogenesis premature ly and reduced subsequent milk yield during established lactation.