Quantitative analysis of behaviour of grazing dairy cows

Abstract

This research thesis describes the quantitative analysis of behaviour of grazing dairy cows in terms of sward height (SH) in combination with the length of the grazing session (grazing duration, GD), the time of allocation of fresh pasture and the type of carbohydrate supplement offered. A review of the literature (Chapter 2) identified that there was limited information on the combined affects of SH and GD on behaviour, herbage dry matter intake (DMI) and intake rate (IR) of dairy cows grazing sub-tropical pastures and how these interact to influence sward structure. Also, there was limited information on how SH x GD, time of allocation of fresh pasture and type of carbohydrate supplement offered affects the temporal patterns of behaviour and the subsequent time-dependent probabilities. In this current study, 2 levels of SH (10 and 13cm) and 5 levels of GD (1, 2, 4, 8 and 15h) were used to quantify the effects of SH and GD on dairy cow grazing behaviour, IR and herbage DMI. Sward height significantly (P<0.05) influenced total GT such that cows grazing SHI3 swards spent an extra 45min grazing than SHIO cows over the I5h grazing period. There was a significant (P<0.05) asymptotic relationship between GT and GD such that GT increased by 0.45 hIh GD to a maximum at 4h GD, irrelevant of SH treatment. Intake rate declined more rapidly for SH13 cows than SH10 cows but had stabilised for both SH treatments by 4h GD. Irrespective of SH treatment, cows had consumed >70% of their total herbage DMI within the first 4h GD. Quantification of the sward profiles after each SH x GD combination showed that dairy cows grazing kikuyu using the management described in this current study did not graze at random. ... The results from this current thesis highlight the factors that either encourage or discourage grazing by dairy cows and should also help to improve decision tools used for pasture rotation, supplementary feeding and stocking density.