How Forage Scarcity Shapes Nutritional Status and Reproductive Function in Cattle

Abstract

Nutrient restriction caused by limited forage availability can increase the prevalence of negative energy balance (NEB) in cattle. This impacts reproductive function as energy needs are preferentially redistributed to more critical physiological systems. Two experiments analyzed follicular and ovarian health through the measurement of non-esterified fatty acids to indicate metabolic stress in nutrient restricted cattle. The second experiment additionally analyzed responses to follicle stimulating hormone (FSH) in nutrient restricted cattle. In study 1, 18 beef heifers were grouped in pens of three by age, weight, and body condition, and assigned to a treatment group: CON (n=9, 100% hay, cracked corn, corn gluten, mineral, water) or RES (n=9, 60% hay, cracked corn, corn gluten, mineral, water), fed from C-lock feeders (C-lock Inc., Rapid City, SD). The experiment lasted 80 days beginning with a 20-day training period for transition from pasture to c-lock feeders. Animals underwent hormonal synchronization for dominant follicle attainment, which was collected via ovum-pickup probe and aspiration needle. Blood was collected weekly and at the time of follicular fluid collection via coccygeal vein. In study 2, 16 beef heifers were individually penned and selected based on age, weight, and body condition, then assigned to a treatment group: CON (n=8, 100% hay, cracked corn, corn gluten, mineral, water) or RES (n=8, 60% hay, cracked corn, corn gluten, mineral, water), fed in J-bunk feeders. Cattle underwent hormonal synchronization with additional exogenous FSH and were ultrasounded pre- and post-stimulation to assess follicular response under the nutrient restriction. Study 1 determined significant NEFA values within follicular fluid (P<0.05) at replicate 2, and significant NEFA values within the serum at replicate 2, 3, and 4 (P=0.002) with a positive correlation between the two detected (P=0.013). However, the association between these two sets of values was weak (r2 = 0.105). Study 2 determined significant NEFA values at OPU 2, 3, and 4 for serum (P=0.01). The same FSH-stimulated effect on follicle development from small to medium sizes was observed in both the CON and RES treatments. Based on these results, two conclusions can be made: NEFAs are validated in indicating the metabolic status (NEB) in nutrient restricted cattle, and FSH supplementation may be a potential solution for overriding poor nutritional status regarding oocyte recovery in NEB cattle.