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Dialing in on Heifer Reproductive Success

Maureen Hanson


October 12, 2020



When it comes to dairy breeding efficiency, there’s plenty of opportunity in the heifer pen, according to Dr. Luis Mendonca, Ruminant Technical Services Specialist with Merck Animal Health.


Mendonca recently shared his insights via “New Research on Reproductive Management of Dairy Heifers,” a webinar hosted by the Dairy Calf and Heifer Association (DCHA).


According to Mendonca, virgin heifers have different metabolism, physiology and estrous cycle lengths than lactating cows. They also have comparatively higher fertility, which is why many dairies prioritize using sex-sorted semen on their heifers.


But while heifers are perceived as relatively “easy” to breed, Mendonca advised there is opportunity to tighten their conception windows and thus freshen a larger percentage of them at the optimal age.


“Delayed conception for heifers becomes costly, because it leads to more non-productive days on feed,” he said. “It also often causes more calving problems, because they may become over-conditioned, with excess fat in the pelvic canal.”


Mendonca noted the “ideal” heifer-breeding program is not a one-size-fits-all proposition. Rather, there are a number of ways that dairies can improve their heifer reproductive efficiency within the framework of an individual dairy’s labor, facilities and management circumstances. But regardless of the program they adopt, goal-setting is a must.


“Each herd should have a target of what percentage of heifers they want to have pregnant after 150 days from the start of breeding,” he advised, noting that 90% pregnancy achievement in this timeframe would be considered excellent.


As opposed to a Voluntary Waiting Period that is the standard start of most lactating breeding protocols, Mendonca said heifer-breeding requires a Voluntary “Weighting” Period, as they must be of acceptable physical maturity first. He advised following the DCHA Gold Standards goals of 55% of mature body weight at the start of breeding, and 85% of mature body weight post-calving at the start of their first lactations.


Mendonca has seen herds achieve excellent reproductive efficiency in their heifers using both heat-detection-based programs and timed-AI protocols. “Something as simple as treating with prostaglandin every 11 days and breeding on detected heat can work very well,” he stated. “Other herds prefer and have great success with a 5-day, timed AI protocol.” For dairies selecting or re-evaluating their heifer-breeding protocols, he advised following tested programs recommended by the Dairy Cattle Reproduction Council.


With either approach, he said results can be improved even further by adopting technologies such as activity monitoring sensors to more clearly assess estrous activity. When using these systems, he advised following the manufacturer’s instructions carefully, as each one works a bit differently.


Finally, Mendonca reviewed recently published data from Dr. Ricardo Chebel and his team at the University of Florida. In a study of 1,027 Holstein heifers, animals were enrolled when they reached 725 pounds (average age 10.7 months) and fitted with Allflex SCR activity monitors. All heifers were placed on a 5-day, timed AI protocol.


If the activity monitors crossed the threshold indicating heat activity, heifers were inseminated via one of three treatments (1) Conventional semen one hour after they appeared on the heat list; (2) Sex-sorted semen one hour after they appeared on the heat list; or (3) Sex-sorted semen approximately 12 hours after they appeared on the heat list. Those heifers not detected in heat at all after 72 hours received a GnRH injection and were bred via timed AI either one hour later (conventional and early sexed semen groups) or 11 hours later (late sexed semen group).


At palpation 30 days after breeding, Chebel and his colleagues observed a significantly higher conception rate for the conventional-semen group (67.3%) compared to the early sexed semen group (45.2%) and the late sexed semen group (46.8%). Although both sexed semen groups ultimately achieved similar conception rates, fertility was poor for the early sexed semen group until approximately 14 hours post-heat-detection, after which they “caught up” to the late-bred sexed semen group.


Although its 30-day conception rate was much higher, the convention group expectedly produced significantly fewer live heifer calves (about 42%) compared to both sexed-semen groups (about 89%). A full economic analysis by Chebel’s team indicated no significant overall profitability advantage for any of the three strategies – reinforcing Mendonca’s suggestion that there are many ways to customize heifer reproduction programs to achieve the best fit for each individual dairy.


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