|Endecott, R - Montana State University|
|Cox, S - New Mexico State University|
|Rubio, C - New Mexico State University|
|Loest, C - New Mexico State University|
|Hawkins, D - West Texas A & M University|
Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2012
Publication Date: 3/1/2012
Citation: Endecott, R.L., Cox, S.H., Rubio, C.M., Loest, C.A., Hawkins, D.E., Petersen, M.K. 2012. Effects of supplements with increasing glucogenic precursor content on reproduction and nutrient partitioning in young postpartum range cows. Livestock Science 145:109–118. Interpretive Summary: Beef cow reproductive efficiency is a critical factor for sustainability of cow/calf operations because reproduction is the primary factor limiting production. In extensive beef cattle operations a lower percentage of young cows becoming pregnant represent an obstacle to profitability. One reason for a lower rebreeding in young cows is their inability to consume enough energy for maintenance, lactation, growth, and nominal resilience due to their immature body weight. Glucose requirements are increased dramatically due to nutrient demands of lactation and range forage may not provide sufficient amounts of glucose precursors. A two-year experiment was conducted to evaluate metabolic and production responses of 2- and 3-yr-old postpartum range cows to increased supplemental glucogenic. Young cows fed a moderate level of glucogenic precursors exhibited consistent milk production and return to estrus regardless of the effects of year. Strategic protein supplementation with a combination of glucogenic precursors may be best suited for young postpartum range cows grazing dormant forage.
Technical Abstract: Altering nutrient partitioning in young postpartum beef cows from milk production to body weight gain has potential to improve reproductive performance. A 2-yr 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-yr-old postpartum beef cows grazing native range to 2 protein supplements with increasing glucogenic potential (GP). Supplements were fed at 1,135 g·cow-1·d-1 twice weekly for approximately 70 d 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 d 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 d 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. Strategic protein supplementation with a combination of glucogenic precursors may be best suited for young postpartum range cows grazing dormant forage.