Administering exogenous porcine prolactin to lactating sows: milk yield, mammary gland composition, and endocrine and behavioral responses.
Third-parity sows received s.c. injections of sterile water (CTL, n = 12) or 15 mg of recombinant porcine prolactin (pPRL, n = 12) at 0730, 1530, and 2330 from d 2 to 23 of lactation. Litters were standardized to 11 or 12 pigs and were weighed weekly until weaning (d 24). On d 22 of lactation, milk production was estimated, and a milk sample was obtained the next day. Jugular blood samples were collected from sows on d 2, 7, 14, and 21 of lactation. Sows were slaughtered and mammary glands collected at d 24. Injections of pPRL doubled the serum concentrations of prolactin (P < .001) on d 7, 14, and 21 of lactation and decreased IGF-I concentrations on d 14 (P = .07) and 21 (P < .01). Weight, backfat, and milk yield of sows and mean pig weights were not affected by pPRL (P > . 1), yet the mean duration of intervals between nursings was reduced by 4.2 min (P = .06) in pPRL litters (45.9 vs 41.7 min). Dry matter and fat percentages in milk were lower in pPRL sows (P < .01). Weights of parenchymal and extraparenchymal tissues were not altered by pPRL treatment (P > .1). Number of prolactin receptors in parenchymal tissue as well as receptor affinity were similar in both groups (P > .1). Results indicate that virtually all prolactin receptors were saturated in CTL sows. This is probably the reason why additional exogenous prolactin had negligible effects.
Farmer
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Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, Lennoxville, Québec.
Sorensen
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Robert
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Petitclerc
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D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001835:Body Weight; D005260:Female; D007774:Lactation / Q000187:drug effects*; D008321:Mammary Glands, Animal / Q000737:chemistry / Q000187:drug effects*; D008892:Milk / Q000187:drug effects*; D011388:Prolactin / Q000494:pharmacology*; D013552:Swine / Q000502:physiology*
D011388:Prolactin