Braunvieh World Winter 2024

IMPACTS OF GESTATION LENGTH Continued from page 8

ducers to shorten calving windows of certain herd groups based off the sire(s) used during that breeding season. In return, this could reduce labor inputs from checking ma ternity pastures, fuel expenses and help producers make decisions on when to assist during the birthing process. When developing and breeding heifers, the GL component could assist in breeding decisions by avoiding longer GL bulls, which in turn could influence incidence of dystocia. The use of GL could be useful in avoiding issues of dystocia, but there could be negative repercussions if a producer single-trait selected for shorter GL in cattle. A recent study using dairy cattle reported short GL (SGL) calves had increased incidences of stillbirths and morbid ity with increased BRD and digestive issues; whereas long GL (LGL) calves had increased incidences of dystocia and stillbirths (due to increase BW) compared to calves of av erage GL (AGL – calves born between 270 and 282 days). Dams calving in the AGL category had a lower assisted calving percent compared to SGL dams. Furthermore, SGL calves were reported to have higher occurrence of death and culling prior to 300 days of age. Calves born from dams from AGL births showed higher incidence of survivability and becoming pregnant at 500 days of age as compared to those of SGL and LGL, which had re duced numbers in being AI bred (due to death or culling). Further investigation is needed to evaluate the impact of management decisions on GL and the influence on calf performance, outside of the use of GL as a management tool in reducing BW of calves. BW

performance, survivability and calf retention for potential replacements. From ongoing research, GL could poten tially become a focus of interest similar to the current focus on birth weight (BW) and calving ease (CE). Let’s discuss the direct influences of GL and factors that influence the number of days (shorter and longer) on GL. The major influences on varied gestation lengths are cattle breed, calf sex, dam age, dam parity, twinning and ambient temperature effect. Cattle gestation length is around 283 to 285 days but is generally influenced by breed type. British breeds are generally shorter than the average (279 days). Continental breeds are typically around the average and American breeds typically have a longer GL than the other cattle breeds. Sire and dam breeds do have additive effects, as reciprocal matings will typically be the average of the two breeds. The influence of the calf sex of bulls will typically increase GL by one day or more compared to heifer calves. Twinning was reported to reduce GL compared to single births. The final factor that directly affects gestation length is the ambient temperature. Previous research indicates that excessive heat and higher ambient temperature will shorten the GL of the calf, while colder temperatures tend to extend the length of gestation. Last, we need to evaluate GL and its influence on beef cattle production. For producers, the increased under

standing of the influence GL has on our breeding, calf and ranch management may help reduce labor and loss due to dystocia. Foremost, calf heritability of GL has been reported to be a moderately inheritable trait of .25 to .54. How does GL impact the beef operation? Gestation length has a direct additive effect on birth weight (BW), which in turn may negatively influence calving ease (CE) in some aspect. So increased labor may occur. In consensus, as GL is below the average of the breed, BW will typically be lighter, and as GL increases, BW is expected to be heavier. Research has indicated that for every 1 day increase in GL, BW increases by .55 to 0.66 pound. As mentioned earlier, breed type has an influence on final GL, which has the same impact on BW. This may result in increased calving assistance at parturition. How can GL be used as a pre diction tool and help make man agement decisions? Sires have been shown to have moderate to moderately high correlation values on GL. Further research should explore GL in order to more precisely evaluate calving date windows due to sire of re cord. This would allow beef pro

UPDATE

West Texas A&M Sire Evaluation Research Project

As of today, there are five calf crops with some form of data collection or com pleted data sets (fall 2021, spring 2022, fall 2022, spring 2023 and fall 2023). There is a combined total of 601 cows between the fall and spring herd, with a total of 324 calves that have been on feed to date. Dam data recorded were breed type, age and body condition. Incorporated into this project are Angus, Braunvieh, Santa Gertrudis and Simmental bulls. For AI sires, there are 37 bulls with 14 clean-up bulls with the most current data records. The data collected in this project began with AI date through harvest data. Calf data was divided into three groups – calfhood, feeding and harvesting phases. During the calfhood phase, the data collected were

Old 13 Farm, Section, Ala.

AI date, DOB, calf sex, BW and weaning weight. During the feeding phase, the data recorded were finishing weight (FW), residual feed intake, average daily gain (ADG), residual ADG, average dry matter intake, raw feed-to-gain ratio (F:G) and adjusted F:G. For the harvesting phase, data collection included finishing weight, hot carcass weight, Quality Grade, Yield Grade, ribeye area, marbling score, backfat and kidney pelvic-heart fat. As of now, there are no findings we can definitively report besides the effect of calf sex on performance traits, which has been bull calves are heavier (BW through FW) than heifers, and heifers have higher marbling carcasses. BW

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Braunvieh World  Winter 2024