Fertility indices for beef bulls*

Abstract

Young (16- to 30-month-old) beef bulls of 6 different genotypes were assessed for production and reproduction traits at different ages and intervals from single-sire mating. Fertility indices, in the form of multiple regression equations using pregnancy rate as the dependent variable, were derived from these assessments using non-orthogonal analyses of variance and covariance. "Among" and "within" genotype fertility indices showed significant correlations with pregnancy rate. "Within" genotype fertility indices showing significant multiple correlations (p less than 0.01) at 11 (r = 0.75), 8 (r = 0.89), 6 (r = 0.86) and 2 (r = 0.80) months prior to mating. It was found that the most important traits to include in the fertility indices were peripheral LH levels following GnRH stimulation, testicular volume, libido and body weight. In general, the fertility indices showed good correlations with bull reproductive performance and were not significantly affected by bull genotype.

Male Reproductive Traits and Their Relationship to Reproductive Traits in Their Female Progeny: A Systematic Review

“…2006) (Table 1). Perry et al. (1990a) reported that the best fertility indices, which included GnRH‐stimulated LH, were those assessed at 11, 8, 6 and 2 months prior to mating and were collectively significantly correlated with pregnancy rate (P < 0.01).…”

“…This test is simpler than multiple samplings as it requires an initial pre‐injection blood sample, followed by an injection of GnRH analogue, and a subsequent single 0.5 to 1 hourly blood sample. However, there are only a small number of publications describing the use of this test, and except for one study in bulls from 16–26 months of age (Perry et al. 1990a), most studies have only monitored the bulls to yearling age (Moura and Erickson 1997; Bagu et al.…”

The value of trans-scrotal ultrasonography at bull breeding soundness evaluation (BBSE): The relationship between testicular parenchymal pixel intensity and semen quality

“…Improvement in the percentage of progressively motile spermatozoa as the only abnormality observed could be explained by the influence of semen handling on sperm viability and the fact that this is a subjective assessment must not be overlooked [23]. The reliability of semen progressive motility assessment in relation to number of calves born per cow appears limited and requires further investigation [2], [24]. More accurate assessment of semen motility and morphology can be performed by the use of computer-aided semen assessment [23].…”

Relationship among testosterone response to GnRH administration, testes size and sperm parameters in Holstein-Friesian bulls

“…In our opinion, the serum testosterone level depends on the number of Leydig cells (maximal testosterone producing capacity of testis). Fertility indices, in the form of multiple regression equations using pregnancy rate as a dependent variable, were derived from production and reproduction traits of beef bulls in Perry's study (13). Fertility indices showed significant multiple correlation among and within genotype (P < 0.01) at 11, 8, and 6 months prior to mating, r=0.75, r=0.89, r=0.80, respectively.…”

“…The correlation values in this studiy support (Table 3) our previous results (18) in that there was a close correlation between the increased testosterone content in the serum and the testosterone level after GnRH treatment (Table l).This correlation may provide information about the responsiveness of Leydig-cells to LH. Perry et al (13) suggested that the most important traits in fertility are the peripheral LH levels after GnRH stimulation and the testicular volume. In our opinion, the serum testosterone level depends on the number of Leydig cells (maximal testosterone producing capacity of testis).…”