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

Abstract

Objective: Aim of the study was to estimate the lactation persistency (LP) of Rambouillet ewes utilizing five mathematical methods.

Design/methodology/approach: Production records from 45 Rambouillet ewes with an average live weight of 65±7.1 kg, from one to three lambings, with one and two lambs, that were weaned at six and eight weeks of age, were utilized. To estimate 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^be^-ct + ɛ_i, unitless), P₃ (the ratio between milk production in the second third of lactation and that of the first third, in %), P₄ (the ratio between milk production in the third third of lactation and that of the first third, in %), and P₅ (milk production from lactation peak to the end of lactation, in %).

Results: Results of the five methods to estimate LP were: P₁= -6.3± 0.4 mL d ^-1, 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 methods generated estimators whose magnitude was not satisfactory compared to other studies in the literature, because the comparisons were made mainly with dairy ewes and cows studies. In the P₅ method, a standard error greater than that of the estimator itself was obtained.

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