Estimation of lactation persistency in a population of Rambouillet ewes utilizing five mathematical methods: Lactation persistency in Rambouillet ewes

Resumen

Objective: The aim of the study was to estimate the lactation persistency (LP) of Rambouillet ewes using five mathematical methods.

Design/methodology/approach: Production records of 45 Rambouillet ewes were used, with an average live weight of 65±7.1 kg, from one to three lambings, with one and two lambs, which were weaned at six and eight weeks of age. To estimate the LP, the following five mathematical methods were used: P₁ (regression of the rate of decline in milk production after reaching peak production, in mL d^-1), P₂ [-( b +1) ln c], where b and c are parameters of the Wood model (Y_t = at^b e^-ct + ɛ_i, without units), P₃ (the ratio between milk production in the second third of lactation and the first third, in %), P₄ (the ratio between milk production in the last third of lactation, and that of the first third, in %), and P₅ (milk production between the lactation peak and the end of lactation, in %).

Results: Results of the five methods to estimate the LP were: P₁= -6.3± 0.4 mL, P₂= 4.8± 0.1, P₃= 108.9± 3.7%, P₄= 72.0± 3.2%, and P₅= 11.1± 12.7%.

Limitations on study/implications: All the methods generated estimators whose magnitude was not satisfactory compared to other studies in the literature, because the comparisons were made mainly with studies on dairy ewes and cows. In the P₅ method, a standard error greater than that of the estimator itself was obtained.

Findings/conclusions: The most reliable methods to estimate the LP in this population of Rambouillet ewes were P₁, P_2, and P₄.