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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #306166
Title: Heifer body weight gain and reproductive achievement in response to protein and energy supplementation while grazing dormant range forage

Author
item Waterman, Richard
item SAWYER, J - Texas A&M University
item KANE, K - New Mexico State University
item HAWKINS, D - West Texas A & M University
item Petersen, Mark

Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2014
Publication Date: 12/15/2014
Publication URL: http://handle.nal.usda.gov/10113/60074
Citation: Waterman, R.C., Sawyer, J.E., Kane, K.K., Hawkins, D.E., Petersen, M.K. 2014. Heifer body weight gain and reproductive achievement in response to protein and energy supplementation while grazing dormant range forage. Agricultural Sciences. 5:1296-1304.

Interpretive Summary: Development of replacement heifers grazing dormant native range to calve as 2-yr-olds in a semi-arid environment is challenging since grazeable forage may supply an inadequate amount of dietary nutrients. Therefore, supplementation strategies that compliment dormant forage to optimize growth and reproductive performance of range raised heifers may be advantageous. In addition, variability in climate influences forage availability and nutrient denseness in semi-arid regions. Inadequate precipitation during critical times of the year (i.e. forage growing season) can impact relative forage quality and quantity. Furthermore, lack of nutrient adequate forages can limit growth rate and development of heifers. To achieve development goals producers can implement supplementation strategies to supply additional nutrients to offset nutrient inadequacies originating from senescent forages. Supplementation with rumen undegradable protein (RUP) can improve feed intake, ADG, feed conversion, and provide glucogenic precursors to improve glucose status. Propionate salts can be directly fed to supply propionate for gluconeogenesis, when glucose limits metabolic function to potentially enhance weight gain, and nutritional status. Our objectives were to monitor body weight change, nutritional status, attainment of puberty, and conception rates for heifers grazing native winter range in response to protein supplements varying in ruminally degradable protein (RDP) to RUP ratios. A secondary objective was to determine if lighter weight heifers have improved body weight change when provided an isonitrogenous supplement providing additional MJ of energy partially supplied by propionate salt. Additional quantities of supplement (i.e. energy) provided to the lightweight heifers improved ending body weights. Although, the light BW heifers were 26 kg lighter at the initiation of the study these heifers were within 20 and 8 kg of heavier BW supplemented heifers, at the termination of the study. This study indicated that altering RDP to RUP within the amount of protein provided did not change body weight or reproductive performance. Serum urea nitrogen concentrations suggest that supplemental protein may have been fed in excess of requirements and therefore, differences in protein use efficiency would not be expected. However, feeding more supplemental energy (i.e., propionate salt, ground milo and corn) allowed lightweight heifers to become more insulin sensitive, which may have partially allowed for a higher rate of gain than their counterparts while achieving comparable reproductive success.

Technical Abstract: Heifers grazing winter range require supplemental nutrients to compliment dormant forage to achieve optimal growth and performance. A study was conducted to evaluate nutritional environment and effect of different supplementation strategies for developing heifers grazing dormant winter range. Eighty-four Angus crossbred replacement heifers were stratified by body weight (BW) at weaning, allocated to one of six replicated pastures, and randomly assigned one of three supplemental treatments: (1) 908 g/d of a control (LORUP) supplement formulated to provide 340 g'hd-1'd-1 of CP with 130 g of rumen undegradable protein (RUP) and 614 MJ of ME (n = 28); (2) 908 g/d of a RUP supplement (HRUP) formulated to provide 340 g'hd-1'd-1 of CP with 170 g of RUP and 567 MJ of ME (n = 27); or (3) 1814 g/d of a protein and energy supplement (LORUP+E) formulated to provide 340 g'hd-1'd-1 of CP with 120 g of RUP + 100 g of propionate salt (NutroCal™, Kemin Industries, Inc.) and 1222 MJ of ME (n = 29). Body weights were taken in November, with monthly 12-h shrunk BW from January thru April, and again in September (at time of pregnancy diagnosis). Heifer average daily gain (ADG) was similar throughout the developmental period except from d125 to d159 where LORUP+E supplemented heifers had greater gains (P < 0.01) than LORUP and HRUP supplemented heifers (0.33, 0.04, and 0.14 ± 0.05 kg/d, respectively). LORUP+E supplemented heifers had a greater percentage (P = 0.04) of heifers pubertal at time of AI breeding compared to LORUP and HRUP supplemented heifers (57, 29, and 30, respectively). However, no differences were detected in overall pregnancy rates (P = 0.40). This study indicates that feeding more supplemental energy (i.e., propionate salt, ground milo and corn) allowed lightweight heifers to achieve a greater rate of gain at a key period during heifer development and comparable reproductive success may be achieved even for light weight heifers grazing dormant range forages.