PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Nutritional aspects of developing replacement heifers 1

Abstract

Studies in numerous species provide evidence that diet during development can mediate physiological changes necessary for puberty. In cattle, several studies have reported inverse correlations between postweaning growth rate and age at puberty and heifer pregnancy rates. Thus, postweaning growth rate was determined to be an important factor affecting age of puberty, which in turn influences pregnancy rates. This and other research conducted during the late 1960s through the early 1980s indicated puberty occurs at a genetically predetermined size, and only when heifers reach their target BW can increased pregnancy rates be obtained. Guidelines were established indicating replacement heifers should achieve 60 to 65% of their expected mature BW by breeding. Traditional approaches for postweaning development of replacement heifers used during the last several decades have primarily focused on feeding heifers to achieve or exceed an appropriate target BW and thereby maximize heifer pregnancy rates. Intensive heifer development systems may maximize pregnancy rates, but not necessarily optimize profit or sustainability. Since inception of target BW guidelines, subsequent research demonstrated that the growth pattern heifers experience before achieving a critical target BW could be varied. Altering rate and timing of BW gain can result in compensatory growth periods, providing an opportunity to decrease feed costs. Recent research has demonstrated that feeding replacement heifers to traditional target BW increased development costs without improving reproduction or subsequent calf production relative to development systems in which heifers were developed to lighter target BW ranging from 50 to 57% of mature BW.

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: How single nucleotide polymorphism chips will advance our knowledge of factors controlling puberty and aid in selecting replacement beef females1,2,3,4

“…Prebreeding reproductive tract examination may eliminate heifers least likely to conceive (Anderson et al, 1991;Rosenkrans and Hardin, 2003). Dietary manipulation to delay BW gain until late in the development period or develop heifers to less than the recommended 60% of mature weight can be implemented to reduce costs with minimal effect on age at puberty and pregnancy rates (Funston et al, 2012;Perry, 2012). Cow herd nutrition, particularly protein supplementation in late gestation, has been shown to increase pregnancy of subsequently born heifer progeny (Martin et al, 2007;Funston et al, 2010).…”

Effect of development system on growth and reproductive performance of beef heifers1,2

“…Traditionally, the recommendation has been that heifers be developed to reach 60 to 65% of mature BW by the onset of the breeding season (Patterson et al, 1992). However, recent research has demonstrated heifers reaching less than 58% of mature BW by breeding do not display impaired reproductive performance (Funston and Deutscher, 2004;Martin et al, 2008;Funston et al, 2012). In today's beef industry, meeting heifer maintenance and gestation nutrient requirements can increase overall development costs for beef producers.…”

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Factors controlling puberty in beef heifers1

“…Snelling et al (2012) concluded by presenting example analyses to demonstrate how integrating information about gene function and regulation with statistical associations from whole-genome SNP genotyping assays might enhance knowledge of genomic mechanisms affecting puberty and fertility, thereby enabling reliable DNA tests to guide heifer selection decisions. Funston et al (2012), the third speaker for the symposium, discussed nutritional aspects of developing replacement heifers. Traditionally, research has shown that puberty in heifers occurs at a genetically predetermined size (around 60 to 65% of their expected mature BW) and that increased pregnancy rates can occur only when heifers reach their target BW.…”

“…By contrast, altering rate and timing of BW gain can result in compensatory growth periods, providing an opportunity to decrease feed costs, a significant cost associated with beef heifer development. Funston et al (2012) then discussed novel data showing that feeding replacement heifers to traditional target BW increased development costs without improving reproduction or subsequent calf production relative to development systems in which heifers were developed to reduce target BW ranging from 50 to 57% of mature BW.…”

“…The Physiology and Endocrinology Symposium on "Factors controlling puberty in beef heifers" encouraged attendees to consider novel nutritional management approaches to hasten the onset of puberty in beef heifers (Lamb et al, 2011;Funston et al, 2012), to apply basic knowledge gained through research to hormonally manipulate the reproductive process to improve reproductive success (Perry, 2012), and to consider new technologies such as SNP that may play a future role in selecting beef heifers for reproductive success (Snelling et al, 2012). The 2011 Physiology and Endocrinology Symposium enhanced our understanding of the latest nutrition, physiology, and genetic research on puberty in beef heifers.…”