Effects of liveweight and incisor arcade breadth on bite mass of grazing Holstein-Friesian dairy cows

Abstract

Bite mass is the dry matter ingested per prehension bite. It has previously been reported that sward characteristics such as herbage height, density and allowance can affect bite mass in grazing cows. Animal characteristics such as liveweight and incisor arcade breadth may also affect bite mass. Understanding factors that influence bite mass can lead to an improvement in the estimate of dry matter intake of grazed herbage. The aim of this study was to determine the effects of liveweight and incisor arcade breadth on average daily bite mass of grazing dairy cows. The research consisted of two parts. In Part I, 113 multiparous lactating Holstein-Friesian cows were assessed for their 7-d average liveweight and incisor arcade breadth. In Part II, from the 113 cows screened in Part I, 32 cows were selected for use in a grazing experiment. The 32 cows were allocated to one of four groups of 8 cows based on the following factors: light cows (mean liveweight of 542 kg) with narrow incisor arcade (mean of 8.2 cm) (L-N), light cows (mean liveweight of 581 kg) with wide incisor arcade (mean of 9.5 cm) (L-W), heavy cows (mean liveweight of 658 kg) with narrow incisor arcade (mean of 8.2 cm) (H-N) and heavy cows (mean liveweight of 660 kg) with wide incisor arcade (mean of 9.5 cm) (H-W). Each cow grazed in an individual plot and herbage intake was calculated as the difference between estimated pre-and post-grazing herbage mass in each plot, as measured with a rising plate metre. Prehension bites were counted using jaw movement sensors. In Part I, incisor arcade breadth of the cows was between 7.0 and 9.8 cm and liveweight was between 490 and 745 kg. There was no relationship (P = 0.30) between liveweight and incisor arcade breadth of these cows. In Part II, mean bite masses were 0.46, 0.50, 0.50 and 0.49 g DM/bite for LN, LW, HN and HW, respectively and the differences between them were not significant (P = 0.30, SED = 0.03). There was also no effect of liveweight category (P ≥ 0.68) or incisor arcade breadth category (P ≥ 0.72) or their interaction (P ≥ 0.78) on prehension bites, mastication chews or total eating bites. These findings suggest that mechanistic models for estimating bite mass and herbage intake may not need to include liveweight or incisor arcade breadth.