Extended lactation length curves of Holstein and Jersey cattle reared in Brazilian dairy farms.

Abstract

A lactation length (LL) of 305 days in milk (DIM) does not fully represent the reality of milk yield and a great part of lactations extend beyond that period. This study aimed to compare the parameters of extended lactation curves with the traditional 305 DIM, considering parity orders (PO) in Holstein (HOL) and Jersey (JER) cows. Data were collected from 33,524 cows (31,194 HOL and 2,330 JER) across 544 dairy farms in Paraná, Brazil. Cows were classified by PO (primiparous, secundiparous, and multiparous) and LL, defined based on calving intervals of 11 to 13 months (LL305_D), 13 to 15 months (LL365_D), and 15 to 18 months (LL435_D). Wood's model was used to estimate lactation parameters from a non-linear mixed model. Cows in LL435_D started with a higher milk yield (parameter A) than those in LL305_D, with the greatest differences observed in multiparous HOL (3.3 L/d) and JER cows (2.1 L/d). However, the rate of increase in milk yield until peak (parameter B) was lower in extended lactations, decreasing from ~ 0.24 to ~ 0.19 in HOL and from ~ 0.18 to ~ 0.14 in JER when comparing LL305_D to LL435_D, respectively. Extended lactations (LL365_D and LL435_D) showed greater persistency (lower parameter C) in both breeds, with primiparous cows in LL435_D being the most persistent (HOL = 0.0018, JER = 0.0016). HOL cows had higher initial milk yield and parameter B than JER cows across all POs and LLs. Primiparous HOL cows reached peak milk yield 13 days later in LL435_D compared to LL305_D. Total milk yield in the lactation increased, while daily mean milk yield per lactation day decreased with extended LL. Extended lactations improved milk yield persistency and could enhance cow longevity, efficiency, and lifetime production.