Natural service synchronization programs

A common misconception exists within the beef industry: “Synchronization protocols are only for use with artificial insemination (AI) programs.” That statement is not true. Synchronization protocols have potential application for natural-service breeding systems and the benefits are similar: A concise calving distribution with the potential for heifers to be serviced twice in about 30 days versus twice in relatively 40 days.

Increased “bull power” may not be a demand of these programs as bull to heifer ratios of 1:15 and 1:20 are acceptable depending on the experience of the sire. These protocols work most efficiently with non-virgin bulls. Size of the breeding area will also dictate these ratios due to the distance that may need to be traveled by the bull with some grazing systems.

Two estrus synchronization protocols that are relatively low cost and have been effective in combination with natural service include: 1) Feed MGA (0.5 mg/hd/day) for 14 days to heifers and turn bulls in 10 days after MGA withdrawal, and 2) Turn in bulls (day 1 of breeding season) and inject all heifers and cows with prostaglandin F2α (PGF) on day 5.  Advantages of the preceding MGA protocol include no trips through the chute and a portion of the prepuberal heifers will be induced to cycle earlier; however, you have to feed MGA daily for 14 days and each heifer needs to receive the correct dose.  The advantage of the PGF protocol is that you only have a single trip through the chute (PGF injection); however, all the heifers and cows need to be cycling in order to respond to PGF.  Prepuberal heifers and/or noncycling cows will not respond to PGF since they do not have a corpus luteum.  Once you become comfortable with implementing an estrus synchronization protocol in combination with natural service it is not difficult to make the next step to using AI instead of natural service.

Pregnancy rates should be relatively comparable to those of synchronized AI systems. For natural service, expected pregnancy rates are normally 60 to 70% during 21 days of breeding assuming the bulls are fertile and that 100% of the heifers and cows are cycling.  However, a pregnancy rate of 60 to 70% over 21 days is unusually high for natural service since rarely are all the heifers and cows cycling at the start of the breeding season.

Cattlemen without AI training skills, facilities, labor resources or the time availability can still take advantage of the benefits of beef synchronization protocols used in conjunction with natural-service breeding programs. Therefore, the ultimate goal of increasing the proportion of females that conceive early can be achieved with natural service through the use on estrous synchronization.

Source: Jim Krantz

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