Supplementation with whole sunflower seeds before artificial insemination in beef heifers

Professional Animal Scientist, Sep 2002 by Funston, R N, Geary, T W, Ansotegui, R P, Lipsey, R J, Paterson, J A

Supplementation with Whole Sunflower Seeds Before Artificial Insemination in Beef Heifers1

Abstract

The objective of this study was to evaluate synchronization and pregnancy rates of beef heifers supplemented with 0.91 kg of whole sun flower seeds for 0, 30, or 60 d before Al. Beef heifers from four locations (n = 1,014) were assigned by BW to treatment (within location) and randomly to AI sire. Heifers at Location 1 (n = 176; mean BW = 332 kg) received either 0- or 60-d sun flower seed treatments. Heifers at Location 2 (n = 397; mean BW = 334 kg) were fed sunflower seeds for 0, 30, or 60 d. Heifers at Locations 3 (n = 211; mean BW = 345 kg) and 4 (n = 230; mean BW = 343 kg) received 0- or 30-d sun flower seed treatments. Within location, diets were

formulated to be isocaloric and isonitrogenous. All heifers received melengesterol acetate (0.5 mg/d per head) for 14 d followed 19 d later by an injection of prostaglandin F^sub 2(alpha)^ (PGF) (25 mg). Heifers were bred by AI according to the AM/PM rule except on d 3 when all heifers that had not exhibited estrus were artificially inseminated in mass. Neither 72-h estrous response nor pregnancy rate was affected (P>0.10) by 30- or 60-d sun flower feeding. In summary, feeding 0.91 kg of whole sun flower seeds for either 30 or 60 d before AI did not improve estrous response or pregnancy rate when compared with controls.

(Key Words: Estrous Synchronization, Heifers, Fat Supplementation.)

Introduction

Proper nutrition is important for adequate growth and development of replacement heifers to ensure that heifers are at puberty and can conceive early in the breeding season. Yearling heifers that conceive early in the breeding season have a greater lifetime productivity than heifers that conceive later in the breeding season (6). Replacement heifer development can be a major cost to a beef cattle operation, and, therefore, it is desirable to minimize inputs and achieve acceptable pregnancy rates. Heifer development systems are generally forage based; however, nonstructural carbohydrates, such as found in cereal grains, are generally required at some point in the feeding period to achieve BW gains needed for puberty before the breeding season. Supplemental lipids have been used to increase energy density of a ration and avoid the potential negative effects on forage digestion (3) that are associated with starch supplementation (2). Supplemental lipids may also have direct positive effects on reproduction in beef cattle, independent of their energy contribution. Supplemental dietary fat has previously been shown to increase serum and follicular fluid cholesterol, serum progesterone, lifespan of induced CL, and number of beef cattle ovulating (8). Lammoglia et al. (5) found that heifers fed safflower seeds (4.4% dietary fat) for 162 d tended (P=0.08) to reach puberty at the beginning of the breeding season in greater percentages than heifers fed no added dietary fat, but there was no difference in overall pregnancy rate. The diet x sire breed interaction suggested that the response to fat supplementation might be breed dependent; however, heifers fed supplemental fat also had greater cholesterol and progesterone concentrations than heifers not fed supplemental fat. It was hypothesized that a shorter feeding period might have been more effective in improving reproductive performance in replacement heifers. Therefore, the objectives of this study were to evaluate the effects of supplemental dietary fat on estrous synchronization and pregnancy rates in beef heifers.

Materials and Methods

Beef heifers, primarily of British breed composition [body condition score (BCS) = 5 to 6 on a 9-point scale, where 1 = emaciated to 9 = obese], from four locations (n = 1,014) were assigned by BW to treatment (within location) and randomly to AI sire. Whole sunflower seeds (0.91 kg/d per head) were included in a total mixed diet for 60, 30, or 0 d before prostaglandin F^sub 2(alpha)^ (PGF) injection. Heifers at Location 1 (n = 176; mean BW = 332 kg) received either 0- or 60-d treatments. Heifers at Location 2 (n = 397; mean BW = 334 kg) were fed sunflower seeds for 0, 30, or 60 d. Heifers at Locations 3 (n = 211; mean BW = 345 kg) and 4 (n = 230; mean BW = 343 kg) received 0- or 30-d treatments. Within location, diets were formulated to be isocaloric and isonitrogenous (Table 1). All heifers received melengesterol acetate (0.5 mg/d per head) for 14 d followed 19 d later by an injection of 25 mg PGF (dinoprost tromethamine; Lutalyse(R); Pharmacia Upjohn Company, Kalamazoo, MI). Heifers were bred by AI approximately 12 h after estrus except on d 3 when all heifers that had not exhibited estrus were inseminated. Pregnancy status was determined by transrectal ultrasonography approximately 40 d after AI. Heifers were weighed approximately 60 d before and at the time of PGF administration, except at Location 3, where BW were taken 30 d before PGF administration to determine whether diet affected ADG.

Two blood samples were collected at a 1-wk interval from heifers assigned to the 60-d treatment diet and the control diet before the beginning of sunflower feeding at Location 2. Blood samples were analyzed for progesterone using coated tubes (Kit TKPGX; DPC, Los Angeles, CA) as described by Bellows et al. (1) to determine percent cycling before treatments were imposed.

Data were combined for Locations 1 and 2 to test the effect of 0- and 60-- d sunflower feeding. Data from Locations 2, 3, and 4 were combined to test the effect of 0- and 30-d sunflower feeding. Data were analyzed using PROC MIXED of SAS (7). Location, treatment, and method of Al (bred on estrus or timed) were fixed effects, and sire was considered a random source of variation. The model was reduced by backward elimination of nonsignificant interactions until only the main effects remained.