SG_USA_March_2023

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SANTA GERTRUDIS

BREEDING SOUNDNESS EXAMS ARE STILL IMPORTANT

By Randy L. Stanko, Ph.D., Texas A&M University-Kingsville

T he only reproductive trait that sur passes the low heritability threshold is scrotal circumference (SC), and we have an expected progeny dif ference (EPD) for that trait. Scrotal cir cumference is considered a moderately heritable trait (0.26-0.53) and cattlemen should consider selecting herd sires with larger SC and higher SC EPDs. Daily sperm production, sperm motility and percentage normal sperm in young bulls is highly correlated (0.72-0.92)

bulls were used for breeding until approximately 24-months of age in this herd during those years of data collection. The results revealed a positive correlation between SC and sperm motility and between SC and sperm morphology in the younger bulls (16- and 20-months-old) only. The percentage of bulls passing the BSE was positively correlated with SC at all ages. The rate of bulls passing the BSE increased over the 10 years. The increase in percentage of bulls passing the BSE was most dramatic in the 16-month-old bulls. They increased from 29.6 percent in year one to 61.6 percent in year eight, proving that bull fertility can be a selected trait. Similarly, SC increased over the 10 years in bulls passing the BSE. Sperm motility scores (subjective measure) in this study were lower in the younger bulls, but sperm morphology was not different between ages of the bulls. In this study, sperm morphology had the highest correlation with BSE score in all ages of bulls. The study speculated that if more selection emphasis is placed on sperm morphology then, perhaps, sperm motility will follow. The bottom line is this data indicates that fertile Santa Gertrudis bulls can be identified by using a minimum SC and the BSE as early as 16-months of age. Moreover, adhering to standards makes it possible to increase the proportion of bulls that will meet the standards in future generations. Yes, BSEs are still important.

with SC. Other than SC, reproductive traits and reproductive performance are pretty much the responsibility of cattle man agers. An annual breeding soundness exam (BSE) with culling and judicious culling of sub-fertile females raised in “your envi ronment” is a great place to begin improving reproduction. Often it helps to look back at history to give us confi dence in managing our present and future. This happened to me recently when I came across some Santa Gertrudis sire research data published in the late 1980s. The research was conducted on a large number of Santa Gertrudis bulls (n=8,861) over a 10-year period. Even though this data was collected more than 30 years ago, and with very different cattle than we have today, the results can provide confidence in the chute-side BSE. Moreover, this data indicated that using selection criteria, including a minimum scrotal circumference and the ability to pass a BSE, allows producers to evaluate and select prospective herd sires between 16 and 20 months of age. Most important, both the percentage of bulls passing the BSE and bull SC increased (due to testing and selection) over the 10 years in this herd. Briefly, BSE results used to select Santa Gertrudis breeding bulls were analyzed in retrospect to determine the effect on bulls in future generations. Bulls were tested at three ages: 16 months (n=1,936), 20 months (n=3,111) and at maturity ( ≥ 24 months, n=3,814). Any bull failing the BSE or not meeting the minimum SC was culled from the herd. All semen samples were collected by electroejaculation. Sperm motility and morphol ogy was determined in a chute-side field laboratory. Sixteen month-old bulls were required to have an SC ≥ 30 cm. At first, 20-month-old bulls needed to have an SC ≥ 30 cm but was later increased to an SC ≥ 32 cm minimum. All mature bulls needed an SC ≥ 35 cm to be considered eligible for BSE. No

The bottom line is this data indicates that fertile Santa Gertrudis bulls can be identified by using a minimum SC and the BSE as early as 16-months of age.

Hefte Ranches, Hondo, Texas

George West, Texas (361) 566-2244 lacampanaranch.com campana@granderiver.net

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SANTA GERTRUDIS USA