Feed costs make up a significant portion of expenses on a commercial dairy operation and minimizing them has become ever more important with the volatility and instability of the current dairy economy. Further, greater push towards agricultural sustainability and minimization of carbon and GHG emissions have heightened the need for selecting for livestock animals that can produce animal products in the most efficient capacity possible. The objectives of this thesis were to explore two different tools: a novel trait for its association with feed intake and a phytogenic feed additive. Individual animal feed intake is needed to generate breeding values to improve feed efficiency, but unfortunately it is costly and difficult to measure. Thus, the first study assessed the use of activity data collected from milking collars as a potential indicator trait for feed intake. Activity data were collected from milking collars on 1630 cows (1524 Holsteins and 105 Jerseys). Activity data were collected in 2-hour intervals, resulting in 12 measurements per day which were summed to daily measurements. A set of 708 cows had individual feed intake recorded across 33 contemporary groups via the Calan Broadbent Feeding System (American Calan Inc., Northwood, NH, USA) and activity during these periods. Milking collar activity was significantly associated with feed intake, milk yield, and milk component measures (p < 0.0001). Additionally, sensor activity differed by parity group and stage of lactation (p < 0.0001), indicating that activity changed later in lactation and with age. Activity also differed by breed (Jersey vs. Holstein) with Jerseys exhibiting higher average levels of daily activity (p < 0.0001). Thus, activity measures will likely need adjustment by breed for applications. These findings indicate milking collar sensor activity is associated with feed intake and provides important adjustment factors to facilitate the use of milk collar activity data as an indicator trait for feed intake. The second study evaluated the effect of a commercial phytogenic feed additive (PFA), Digestarom? Dairy (DD) (BIOMIN America, Inc., Overland, KS, USA) on feed intake, production traits, and health. Phytogenic compounds are thought to prevent animal health events and reduction in health events should improve feed efficiency. A total of 108 lactating Holstein dairy cows (parities 1–6; 49–219 days in milk (DIM)) were selected to receive DD or the control supplement in two cohorts (n = 60 and n = 48) in the Calan Broadbent feeding system (American Calan Inc., Northwood, NH, USA) for approximately 40 days. The DD additive was found to significantly increase milk yield, milk fat, and milk protein, and was associated with reduced incidence of health events (p < 0.0004). Additionally, DD effects differed among cattle of different parities and stages of lactation, with greater effects in parity 2 and 3+ and greater than 175 DIM for milk yield (p < 0.0001). These findings indicate that DD increased milk yield and components while potentially reducing health events which improves feed efficiency. Further, these results serve as precursors for future studies that will investigate genetic components, such as epigenetic factors, that may be differentially impacted by feeding this additive.
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