Examining Factors of Variance in Energy Metabolism of Dairy Cattle

Variation is thought to occur in the use of dietary energy for production in dairy cattle. First, variance can be observed when new methane mitigation strategies are fed resulting in increased H2 output potentially resulting in downstream effects on estimates of heat production via the Brouwer (1965) equation. Therefore, in chapter 3 a review was created to systematically describe the mathematics and theory behind the Brouwer equation, and rederive a heat production equation to integrate H2 production. Results indicate heat production using the classical Brouwer equation (1965) relative to the rederived equation resulted in an overestimation of heat production ranging from 0.005–0.230 Mcal/d when additives to mitigate CH4 are fed. Chapter 4 analyzes variation in energy use for milk production or reproductive functions resulting from the variation between nutritionist formulated diet and fed ration. Overall, farms overfeed nutrients relative to the formulated diet 92% of the time, and farm to farm variation is large. Also, overfeeding crude protein may have negative implications on pregnancy rate. Outside of diet handling, energetic variation can be attributed to various factors including genetics, and dietary treatment. Thus, the respective contribution of among-animal, dietary, and experimental variance to observed variation in energy utilization were quantified in chapter 5. We observed among-animal variance in CH4, and tissue energy losses are likely due to inherit animal differences with these differences increasing when expressed per unit of dry matter intake. Subsequently, in chapters 6 and 7 evaluates the maintenance energy requirements and fasting heat production for heifers, and for multiparous dairy cattle with differing body condition score. Jersey heifers maintenance energy requirements were observed to be 8% greater per unit of metabolic body weight relative to requirements within the dairy NASEM (2021) model. Although body condition score did not influence maintenance requirements (NELmaint = 0.10 × BW0.75) when expressed per unit of metabolic body weight, total heat production increased with increasing body condition score. Advisor: Paul J. Kononoff