Expanding the dairy herd in pasture-based systems: The role of sexed semen use in virgin heifers and lactating cows

A model was developed to examine the effects of sexed semen use in virgin heifers and lactating cows on replacement heifer numbers and rate of herd expansion in a seasonal dairy production system. Five separate herds were established according to the type of semen used: conventional frozen-thawed (Cony), sexed fresh semen used in lactating cows for the first 3 wk of the breeding season (SFre1), sexed frozen-thawed semen used in lactating cows for the first 3 wk of the breeding season (SFro1), sexed fresh semen used in lactating cows for the first 6 wk of the breeding season (SFre2), or sexed frozen-thawed semen used in lactating cows for the first 6 wk of the breeding season (SFro2). In the Sol, SFrel, SFro2, and SFre2 herds, sexed semen was used for the first and second artificial insemination in virgin heifers. Pregnancy rates achieved with sexed fresh and sexed frozen-thawed semen were assumed to be 94 and 75% of those achieved with conventional frozen-thawed semen, respectively. Initial herd size was 100 cows, which was maintained for the first 2 yr of the 15-yr simulation, after which all available replacement heifers were retained to facilitate herd expansion. Two different scenarios of land availability were examined for each of the 5 herds: land available allowed expansion to a maximum herd size of 150 cows (Si), or land available allowed expansion to a maximum herd size of 300 cows (S2). Once maximum herd size was reached, sexed semen use was discontinued and all excess heifer calves were sold at 1 mo old. All capital expenditure associated with expansion was financed with a 15-yr loan. Each of the 10 different options was evaluated in terms of annual farm profit, annual cash flow, and total discounted net profit. The use of fresh sexed semen generated more replacement heifers, leading to faster herd expansion compared with frozen-thawed sexed semen and conventional frozen-thawed semen. Maximum herd size under Si was reached in yr 5, 5, 4, 5, and 7 for the SFre1, SFro1, SFre2, SFro2, and Cony herds, respectively. Under S2, maximum herd size was reached in yr 8, 10, 7, 9, and 14 for the SFrel, SFro1, SFre2, SFro2, and Cony herds, respectively. Total discounted net profit under Si for the SFre2 herd was (sic)4,130, (sic)38,869, (sic)47,231, and (sic)52,089 greater compared with the SFrel, SFro1, Cony, and SFro2 herds, respectively. Under S2, discounted net profit for the SFre2 herd was (sic)44,204, (sic)255,524, (sic)280,373, and (sic)325,815 greater compared with the SFrel, Sol, SFro2, and Cony herds, respectively. The negative effects of the sexed frozen-thawed semen on herd fertility reduced farm profitability and will prevent its widespread use in lactating cows.