Effect of climate conditions on fat and protein yields in small dairy ruminants.
- Citation:
- Ramón, M., H. M. Abo-Shady, C. Díaz, A. Molina, M. D. Pérez-Guzmán, J. M. Serradilla, M. Serrano, and M. J. Carabaño, "Effect of climate conditions on fat and protein yields in small dairy ruminants.", 64th Annual Meeting of the European Federation of Animal Science. EAAP. Nantes, France., 2013.
Abstract:
The model initially proposed for dairy cattle to evaluate the impact of heat stress (HS) on milk yield assumes a comfort zone and a zone above a threshold (To) with a linear decrease of production. Studies with this or other models are scarce for small dairy ruminants. Our aim was to examine the shape of response on production associated with increasing values of temperature and a temperature and humidity index (THI) in two breeds. A total of 1,675,886 and 116,258 daily fat and protein yields from the official milk recording of 191,641 Manchega ewes and 11,259 Florida goats, respectively, were used. Average (Tave) and maximum daily values for temperature and THI at the test day were obtained from the Spanish Meteorological Agency. Two data sets, all and only high producing animals (above 1.5 SD) were analyzed per breed. Two types of models were used, one fitting splines (SP) with one knot at To and a linear slope b afterwards, and another fitting Legendre polynomials (LP) of varying order (up to cubic). Models included herd-year of test day, number and stage of lactation, age of the animal at recording, prolificacy, milking time and animal apart from the temperature/THI functions. For Tave, To was found at 29ºC for sheep and at unexpectedly small values around 10 ºC for goats. Values of b were low in general, but larger for highly productive ewes, with declines of up 16g/ºC of protein. LP models resulted in better fits in both species, lower HS thresholds for sheep and similar for goats. It was also interesting the assessment of thresholds for cold stress in sheep. The latter might suggest the existence of a zone of comfort with two thresholds, outside of which yields decrease.
Notes:
n/a