Influence of cumulative feed intake during early and mid-lactation on luteinizing hormone secretion and weaning-to-estrus interval in primiparous sows

Twelve pregnant gilts were assigned to a completely randomized block design with two treatments in two blocks (2 farrowing groups). The treatments wer e a feeding amount of 6 kg or 2 kg/day provided during lactation. The lacta tion diet contained 18.6% crude protein, 1.0% lysine, and 3.27 Mcal/kg meta bolizable energy (as-fed basis). Litters were weaned at 2100 on day 21 afte r farrowing. Blood samples for luteinizing hormone (LW) measurements were t aken at 15-min intervals for 8 hr on day 12 of lactation, and samples for g lucose and insulin were collected at I-hr intervals for 3 hr on day 12. The effects of feed intake treatments on LH pulse frequencies (2.9 vs 0.7) and insulin concentrations (15.0 vs 8.9 IU/mL) were found (P<0.05) on day 12 o f lactation. In regression analysis, greater cumulative feed intake fi-om 1 to 12 days was associated with higher insulin concentrations (P=0.04), gre ater LH pulse frequencies (P=0.01) on day 12 of lactation, and shorter wean ing-to-estrus intervals (WEI) (P=0.03). Furthermore, an association between insulin concentrations and LH pulse frequencies was found on day 12 of lac tation (P=0.01). Using regression models for weaning-to-estrus interval, wh en each cumulative feed intake from 4 to 21 days was used as an independent variable, the R-2 values increased from 0.24 to 0.37. These results sugges t that feed intake during early and mid-lactation influences LH secretion a s early as day 12 after farrowing, and is associated with shorter WEI. This research also indicates that feed intake from 4 to 12 days of lactation is more important than that during the first few days after farrowing.