Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 10, 2009
Publication Date: June 15, 2009
Citation: Mulliniks, J.T., Cox, S.H., Kemp, M.E., Endecott, R.L., Waterman, R.C., Vanleeuwen, D.M., Petersen, M.K. 2009. INCREASING GLUCOGENIC PRECURSORS IN RANGE SUPPLEPMENTS IMPROVES REPRODUCTIVE EFFICIENCY AND PROFITABILITY IN YOUNG POSTPARTUM RANGE COWS IN YEARS 2000 TO 2007. Western Section of Animal Science Proceedings 60:76-80. Interpretive Summary: Achieving reproductive efficiency in a beef cow herd is a critical factor for beef cow/calf producers to be a sustainable operation. 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 my not provide sufficient amounts of glucose precursors. Therefore, the objective of this experiment was to compare measures of reproductive efficiency such as, pregnancy rate, days to first estrus, calf weight per cow exposed, as impacted by 3 different postpartum supplementation strategies increasing in glucogenic potential and assess economic viability of a 2- and 3-yr-old cows grazing native range. Results indicate that by increasing glucogenic precursors in range supplements decreased days to first estrus and improved pregnancy rates in 2- and 3-yr-old cows by apparently repartitioning nutrients away from lactation. Additionally, the increase in pregnancy rates for cows fed propionate salts offset the higher cost of the supplement by increasing calf crop the following year which increased ranch revenue compared to the other supplements fed in this study.
Technical Abstract: Reproductive efficiency in young beef cows is often compromised due to a mismatch of physiological demands and suboptimal environmental conditions. Studies conducted at the Corona Range and Livestock Research Center from 2000 to 2007 evaluated 3 postpartum supplement strategies increasing in glucogenic precursors (GP). Reproductive variables, milk production, and serum metabolites were used to assess supplement effectiveness and economics associated with young beef cow production (n = 379) on native range. Supplements were individually fed 2×/wk at 1135 g/d (2003-2004) or 908 g/d (all other yr) and provided: 1) 327 g CP, 109-118 g undegradable intake protein (UIP), 44-47 g GP (CON); 2) 327-341 g CP, 142-157 g UIP, 57-70 g GP (BP); 3) 327 g CP, 151-173 g UIP + 40 – 100 g of propionate salt (NutroCal, Kemin Industries, Inc.), 93-141 g GP (P). Blood samples were collected 1×/wk (2000) or 2×/wk (2001-2007) for progesterone analysis to estimate days to first estrus. Cows were exposed to bulls for 60 d or less and pregnancy was confirmed by rectal palpation at weaning. Number of days to first estrus after calving decreased and pregnancy rates increased linearly (P < 0.02) with increasing supplemental GP. Milk production exhibited a quadratic (P = 0.04) response to increasing GP with cows fed B producing the most amount of milk (5920, 6812, and 6217 ± 421 g/d for CON, BP, and P, respectively). Total kg of calf weaned per cow exposed for the supplemental year and subsequent year was greater (P = 0.07) for cows fed P than the other supplements (418, 410, and 435 ± 40 kg for CON, BP, and P, respectively). These data suggest feeding young cows additional GP in the form of propionate salts allows for repartitioning of nutrients away from milk production and towards reproduction.