Seminal characteristics in beef bulls supplemented with rumen bypass fat

INTRODUCTION

The quality of the semen is one of the factors most important in success of reproductive biotechnologies (artificial insemination, fixed time artificial insemination, embryonic transfer and in vitro fertilization). The level of dietary energy has been suggested as the main nutritional factor determining the effects on sperm quality. However, incorporation of bypass polyunsaturated fatty acids (PUFAs) in diets can improve semen quality due to caloric effects on energy balance and the non-caloric effects related to synthesis of testosterone in Leydig cells and phospholipids in spermatozoa cell membrane. The supplementation with sources of polyunsaturated fatty acids can improve the characteristics of spermatic membrane that give resistance to the process of stress, such as freezing and thawing. The hypothesis is that transfer of polyunsaturated fatty acids (PUFAs) from diet to sperm increase PUFAs in sperm membranes, increase semen quality and fertilizing ability. The objective of this study was evaluate the effect of bypass fat supplementation on fresh semen quality characteristics of Angus e Hereford bulls.

MATERIALS AND METHODS

Location: PROGEN - Collection Central Office and Semen Processing - Dom Pedrito - RS - Brazil.
Twenty Hereford, Angus, Brangus and Braford mature bulls (950 kg average body weight) were used in a completely randomized design
Bulls were arbitrarily assigned to one of two treatments: bypass fat (BF) or energy (ES) supplementation for 75 days.
Bulls were kept individually in paddocks and fed diets with similar level of protein and energy consisting of : green forage, commercial concentrate, mineral salt, and supplemental rumen bypass fat (BF) or energy supplement (ES). Bulls in BF treatment (10) received Megalac-E® (200 g/day) and ES treatment received Cassava (Manihot esculenta, Crantz) meal (750 g/day) (Table 1).
Samples collection: Bulls were naturally stimulated by cows and semen collected with an artificial vagina every fifteen days.
Parameters of seminal quality evaluated: Volume, concentration, mass mobility, individual mobility, vigor.

Data were analyzed using the GLM procedure of SAS. For all data repeated measured analysis of variance was used to determine main effects of treatments, breed, collection week and interactions. The treatments were compared using a Tukey test (α = 0.05).

RESULTS

The treatments did not affect initial and final body weight and average daily gain of bulls (p>0.05) (Table 2).
Bull breed and collection week did not influence the semen characteristic (p>0.05).
The values obtained on seminal quality parameters suggest medium to good quality semen.
The supplementation with rumen bypass fat or Cassava meal did not affect ejaculate volume, spermatozoa concentration and mass motility in fresh semen (p>0.05) (Table 3).
Semen of bulls supplemented with rumen bypass fat had a 10% increase in individual motility (83.2 vs 75.8%) and lower variability than semen of bulls supplemented with cassava meal (p=0.05) (Table 3).
Semen of bulls supplemented with rumen bypass fat had a 11% increase in vigor (3.62 vs 3.26) than semen of bulls supplemented with cassava meal (p=0.07) (Table 3).

CONCLUSIONS

Energy supplementation of bulls in the form of rumen bypass fat rich in polyunsaturated fatty acids (PUFAs) increased straight progressive motility (individual motility) and velocity (vigor) of spermatozoa.

ACKNOWLEDGEMENTS