Combining extended lactation with sexed semen in a dairy cattle herd: Effect on genetic and total economic return

• Extended lactation has shown economic benefits in dairy herds, but this strategy may affect the genetic lag between the production cows at herd level and the semen bulls unfavorably. We hypothesize, that a breeding strategy using sexed semen (SS) will reduce this effect and that SS and extended lactation has synergetic effects on the total economic return. A base scenario reflected an average Danish Holstein herd with 13 months calving interval (CInt) (BASE). Additionally, six scenarios with extended lactations: two with only first parity cows managed for a CInt of 15 (FIRST15) and 17 months (FIRST17), two with only cows in second parity or higher managed for a CInt of 15 (OLDER15) and 17 months (OLDER17), and two with all cows managed for a CInt of 15 (ALL15) and 17 months (ALL17). These were combined with four breeding schemes illustrating different uses of SS within each of the scenarios: SS in 50% genetically best heifers (SS50), 75% genetically best heifers (SS75), all heifers (SS100) and 70% genetically best heifers and 30% first parity cows (SS7030). Beef semen was used when necessary to equalize the number of replacement heifers within extended lactation scenarios. The scenarios were simulated using two stochastic simulation models for estimation of operational returns (SimHerd) and for genetic returns (ADAM). The genetic returns support that extended lactation has an unfavorable effect on genetic lag in SSO, because the generation interval among breeding females increases when extended lactation is introduced. Compared to BASE/SSO most combinations of SS and extended lactation, with the exception of ALL17 combinations increased genetic returns as a result of decreased generation interval. Across extended lactation scenarios, reductions in genetic return relative to BASE was between (sic)1 (FIRST15) and (sic)12 (ALL17) per cow year within each scenario of SS. With increased use of SS, the genetic returns increased from (sic)4 (SS50) to (sic)12 (SS7030) per cow year, compared to SSO within each scenario of extended lactation. In total economic return, the use of SS had effects between + (sic)5 and + (sic)29 per cow year due to increased use of beef semen, thus more sales of slaughter calves. Except for OLDER15 and OLDER17, the extended lactation scenarios within each scenario of SS increased total economic returns as well. In conclusion, the genetic lag caused by extended lactation can be reduced using SS, although there was no synergetic effect between SS and extended lactation on the total economic return.

Ämnesord

LANTBRUKSVETENSKAPER  -- Husdjursvetenskap -- Husdjursvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Animal and Dairy Sience -- Animal and Dairy Science. (hsv//eng)

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