Modelling the effect of stocking rate on the lactation profiles of grazing Holstein-Friesian dairy cows using cubic splines

Adediran, S.A., Ratkowsky, D., Donaghy, D.J., and Malau-Aduli, A.E.O. (2008) Modelling the effect of stocking rate on the lactation profiles of grazing Holstein-Friesian dairy cows using cubic splines. Current Topics in Dairy Production, 13. pp. 25-32.

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The objectives of this study were to compare the lactation profiles and performance of dairy cows on dryland versus irrigated pastures at different stocking rates with or without grain supplementation using cubic splines model. The data consisted of 12,939 records (572) lactations of mixed parity cows. Editing criteria of the data excluded records without birth dates, calving dates, days in milk less than 5 or greater than 306 or cows with test days lesser than 4, while parities greater than 3 were pooled. Restricted maximum likelihood procedures in ASReml were utilised to analyse the data using an animal model that fitted days in milk (DIM), stocking rate, year, parity and calving season as fixed effects. Random effects included cow and the splines of DIM nested in stocking rate, year, parity, calving season, while age at calving was used as a covariate. Stepwise regressions of all explanatory variables and their interactions were tested before arriving at a parsimonious model. Results indicated that cubic splines adequately modelled the bi-weekly milk yield data with low residuals and uncorrelated coefficients which is attributed to the great flexibility of the model. Without supplementation, mean milk yield did not differ much but was slightly higher in cows grazing at 2.5-3.5 cows/ha stocking rate (SR) compared to cows stocked below at 2.0 c/ha and above at 4.0 c/ha.The results demonstrate the accuracy of cubic splines in modelling lactation and that higher stocking rates can improve the efficiency of pasture utilisation when coupled with adequate grain supplementation. Without supplementation the 2.9 c/ha (dryland) and 3.5 c/ha (irrigation) treatments respectively were the best overall but the 3.4c/ha (irrigation) plus grain supplement was better than both. The poor performance of the 4.0 c/ha treatment highlights the potential of substitution, pasture wastage and the importance of pasture management skills in pasture-based grazing systems. The results confirmed that the key to improving profitability is optimising pasture production and then matching feed demand to feed supply with an appropriate stocking rate, to ensure that both pasture and supplements are utilised efficiently. Other potential lessons and scope for future studies are; to minimise pasture damage in wet conditions and adopting good reproductive management such as earlier calving of dryland herds to take advantage of better pasture growth in the more favourable season depending upon local growth patterns and other management practices.

Item ID: 55014
Item Type: Article (Short Note)
ISSN: 1326-489X
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Proceedings of the Dairy Research Foundation Symposium, Sydney, NSW, Australia, 2008.

Date Deposited: 04 Dec 2018 01:46
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0702 Animal Production > 070201 Animal Breeding @ 100%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8303 Livestock Raising > 830302 Dairy Cattle @ 100%
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