Abstract
It has been well established that cow/calf plane of nutrition affects performance of not only the dam and the nursing calf, but also the fetus in utero. Stocking rate is the foundational grazing management decision, and it affects quantity, quality, and persistence of perennial forages. Recent research has highlighted the effects of stocking rate on perinatal programming in beef cattle. Our objective was to evaluate the implications of these effects on grazing management for southeastern US beef cows maintained primarily on warm season perennial grasses. We utilized records from 34 years of F1 (Hereford or Angus x Brahman) cow and Simental-sired calf performance data from the Texas A&M AgriLife Research Center in Overton, TX and 12 years of diet quality predictions via fecal near infrared spectroscopy from the Grazingland Animal Nutrition Laboratory in College Station, TX to inform two case study scenarios: a) high stocking rate-low plane of nutrition (HL), and b) low stocking rate-high plane of nutrition (LH). Case study nutritional analyses utilized a Brahman x British F1 January to March calving cow (522 kg standard reference weight), with an 8.6 kg peak milk yield at 45 days post parturition. Descriptive statistics (mean, standard error, quartiles) were calculated for monthly diet quality values. The HL scenario was conducted with 1(st) quartile diet quality values; LH utilized 3(rd) quartile values. Within each respective plane of nutrition, stocking rate was accounted for by setting a maximum daily dry matter intake that resulted in a net loss (HL) or gain (LH) of 1 body score over the course of a summer grazing period (i.e. early lactation to weaning). Similar to previous stocking rate analyses, HL in a given production year resulted in lower individual animal performance but greater production per unit of land area as compared to LH. Costs of production (replacement females, supplemental feed, lower forage production) associated with HL will likely reduce or offset the differences in net returns to the cow herd between each scenario over time. Additionally, epigenetic effects to subsequent offspring will reduce long-term productivity in HL. Grazing management decisions for the pregnant/lactating cow affect: a) the cow’s ability to maintain pregnancy, b) growth and development of the suckling calf, c) growth and development of the fetus in utero, and d) maintenance of cow body condition to prepare for parturition. Based on our long-term data, HL will often be more profitable in a given production cycle compared to LH, but will adversely affect subsequent offspring performance and forage persistence; effects that will accrue for the entire beef industry.