Cattle are differentially adapted to nutritional environments. The most sensitive measure of adaptation is reproduction of first-calf heifers. We studied the role of maturation rate and milk production on reproductive performance of first-calf heifers allowed different levels of herbage in semiarid rangeland

Holloway, J. W.

Owens, M. K.

Warrington, B. G.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings XX International Grassland Congress Phenotype X Herbage Allowance Interactions in Reproduction of First Calf Heifers Grazing Semiarid Rangeland J. W. Holloway Texas A&M University B. G. Warrington Texas A&M University M. K. Owens Texas A&M University Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, and the Weed Science Commons This document is available at https://uknowledge.uky.edu/igc/20/themeA/7 The XX International Grassland Congress took place in Ireland and the UK in June-July 2005. The main congress took place in Dublin from 26 June to 1 July and was followed by post congress satellite workshops in Aberystwyth, Belfast, Cork, Glasgow and Oxford. The meeting was hosted by the Irish Grassland Association and the British Grassland Society. Proceedings Editor: D. A. McGilloway Publisher: Wageningen Academic Publishers, The Netherlands © Wageningen Academic Publishers, The Netherlands, 2005 The copyright holder has granted the permission for posting the proceedings here. This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. Offered papers 137Phenotype x herbage allowance interactions in reproduction of first calf heifers grazing semiarid rangeland J.W. Holloway, B.G. Warrington and M.K. Owens Texas Agricultural Experiment Station, 1619 Garner Field Road, Uvalde, TX 78801, USA, Email: jw-holloway@tamu.edu  Keywords: herbage allowance, growth curve, milk production, environmental interactions   Introduction  Cattle are differentially adapted to nutritional environments. The most sensitive measure of adaptation is reproduction of first-calf heifers. We studied the role of maturation rate and milk production on reproductive performance of first-calf heifers allowed different levels of herbage in semiarid rangeland.     Materials and methods  Data was collected over 4 y for 197 primiparous Brahman x Hereford F1 females grazing a semiarid Acacia savannah (Study 1, 290 lat. 990 52' long. 52 cm rain/y).  Females were the residual from 345 heifers allotted at weaning each year to 4 pastures (1,950 to 6,100 ha) with 4 stocking rates (17 to 146 kg body weight [BW]/ha) to give a total of 16 herbage allowances (HA) over the four years (400 to 2,800 kg DM/100 kg BW).  Calving (Jan.-Mar) was as 2- and then as 3-y olds. The HA was the mean of about 55 monthly hand clipped and visually estimated 0.5m2 quadrats/pasture.  Maturation rate (k [-kg/d per d; this is the rate of decline in weight accretion and is negatively correlated with frame size] from Wt=B+A loge-kt of Brody, 1945) was computed (Beltran et al., 1992).  First-lactation milk production (MP) was the mean of three estimates based on weighing calves before and after suckling. Distance traveled/d was estimated in Study 2 for 72 GPS-collared cows varying in frame size and allowed 1,200 ha pastures.  Results  Figures 1 and 2 show the probability of a heifer being bred (PB = 1.28 -(log (-30.7149 + 0.0171771*HA + 398.689*k + 0.0143144*MP - 0.005403*HA*MP - 0.237244*HA*k -120.042*MP*k + 0.071795*HA*k*MP)-0.08)) (Chi Squares, P<.05). For the mean MP, earlier maturing females (EMF, k=0.080) had higher PB at low HA. At high HA, the reverse was true. For late maturing females (LMF, k=0.075), HA influenced PB more than for EMF. In Study 2, for frame sizes 4, 5, 6, 7 and 8 the distances traveled were 4,837, 5,255, 5,541, 5,531, and 5,227 m/d respectively, indicating an asymptote at 6. The frame size in Study 1 was  from 2 to 6. The data suggest that in Study 1 the LMF, with higher frame size, would have traveled further in search of feed. At high HA, the search was successful, resulting in increased PB. At low HA, the search was less successful, resulting in lower PB. In Figure 2, at the mean HA, MP influenced PB much more than k.                  Conclusions  The cow type that gives the best reproductive performance in semiarid rangeland depends on HA.  Late maturing cows have ability to travel further from water and thus acquire more pasture at high HA. At limited HA, this is a detriment because LMF have larger working maintenance requirements and derive little extra feed. Adapted females gave more milk and had greater PB than less adapted females.    References  Brody, S. (1945).  Bioenergetics and Growth.  Reinhold Publishing Corp., New York. Beltran, J.J.. W.T. Butts, Jr., T.A. Olson & M.  Koger (1992) Growth patterns of two lines of Angus cattle selected using predicted growth parameters.  Journal of Animal Science, 70, 734-741. Figure 1  Effect of HA, kg DM/100 kg BW and estimated k, kg/kg/d on probability bred (milk=5 kg/d) Figure 2  Effect of milk, kg/d and k kg/kg/d on probability bred (HA = 1600 kg DM/100 kg BW) 

Phenotype X Herbage Allowance Interactions in Reproduction of First Calf Heifers Grazing Semiarid Rangeland

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Phenotype X Herbage Allowance Interactions in Reproduction of First Calf Heifers Grazing Semiarid Rangeland

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