Effects of supplements with increasing glucogenic precursor content on reproduction and nutrient utilization in young postpartum range cows

Altering nutrient utilization in young postpartum beef cows from milk production to body weight gain has potential to improve reproductive performance. A 2-year study conducted at the Corona Range and Livestock Research Center from February to July in 2003 (n = 33) and 2004 (n = 26) evaluated responses of 2- and 3-year-old postpartum beef cows grazing native range to 2 supplements with increasing glucogenic potential (GP). Supplements were fed at 1135 g∙cow− 1∙ day− 1 twice weekly for approximately 70 days postpartum and provided 1) 341 g CP, 142 g ruminally undegradable protein, 57 g GP (GP57), or 2) 341 g CP, 151 g RUP + 80 g propionate salt (NutroCAL, Kemin Industries, Inc.), 121 g GP (GP121). Supplement × year interactions were observed for days to first estrus (P = 0.04) and 24-h milk production at ~ 60 days postpartum (P = 0.04). Cows fed GP57 took longer to return to estrus in 2004 than in 2003, while cows fed GP121 returned to cyclicity in similar days postpartum regardless of year. Cows fed GP57 produced more milk in 2004 than 2003, but cows fed GP121 produced similar amounts of milk regardless of year. Cows had similar (P = 0.61) glucose half-lives after glucose tolerance test at ~ 55 day postpartum (77 and 68 ± 12 min for GP57 and GP121, respectively). Young cows fed GP121 exhibited consistent milk production and return to estrus regardless of the effects of year.