Online

Miller, Michael Devin

Animal and Veterinary Sciences

2020

Ph. D.

Dry matter intake (DMI) is one of the most important factors affecting lactational performance and health of dairy cows. Control of DMI in dairy cattle is complicated and multifactorial, but we have chosen to prioritize the two main components that primarily drive farm profitability: forage quality and cow comfort. Brown midrib-3 (BM3) genetics in corn silage typically result in greater fiber digestibility and less indigestible fiber, which result in greater DMI and milk production compared to conventional, non-BM (CON) corn silage. Trace minerals may negatively affect fiber digestion by solubilizing in the rumen. Importantly, hydroxy trace minerals (HTM) are less soluble in the rumen compared to sulfate sources (STM). Still, to-date, no models have inputs that reflect social environment factors such as stocking density and feeding frequency. The objectives of this dissertation were to: 1) evaluate the effect of source of corn silage and trace mineral on lactational performance, total tract digestibility (TTD) of nutrients, and rumen fermentation, and 2) create a model that accurately quantifies the effect of management decisions on DMI. The study addressing the first objective (Chapters 2 and 3) investigated the effects of source of corn silage (CON or BM3) and trace minerals (STM or HTM) on lactational performance, TTD of nutrients, and particle passage rates. Sixteen Holstein cows averaging 82 (SE = 3) days in milk were used in a replicated 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments. The dietary treatments were: 1) CON-STM, 2) CON-HTM, 3) BM3-STM, and 4) BM3-HTM. There was no significant interaction between corn silage and trace mineral for DMI and milk yield. Cows fed the BM3 diets had greater DMI and milk yield compared to the cows fed the CON diets. The cows fed the HTM diets had greater DMI than cows fed STM diets. The cows fed the BM3 diets had greater TTD of dry matter (DM) and organic matter (OM) than cows fed the CON diets. Cows fed the HTM diets had a tendency for greater TTD of neutral detergent fiber (NDF) than the cows fed STM diets. Cows fed the BM3 diets had a faster passage rate of small- and medium-sized corn silage NDF particles than cows fed the CON diets. The study addressing the second objective (Chapter 4) created a model that accurately quantifies the effects of stocking density and feeding frequency on behavior and performance of lactating dairy cattle. The foundation of the management model was a time budget. The eating time was predicted using common on-farm measures (NDF content, physically effective NDF, body weight, and milk yield) and had a good predictive ability with a mean absolute error of 39 min/d regardless of parity. Stocking density affected lying time, which accounted for 76% of the variance in lying time. The adjusted lying time was then used to predict a milk yield, which accounted for 36% of the variance in milk yield. The peuNDF240 accounted for 60% of the variance in DMI. Brown midrib-3 corn silage enhanced DMI, milk yield, TTD of OM, and greater passage rate of corn silage particles. Hydroxy trace minerals improved DMI, tended to improve TTD of NDF. The management model appeared to be a useful tool, although more data and research are needed to validate the model. In the future, hopefully, both forage quality and management decisions will be included in the same nutritional model to predict feed intake more accurately.