Replacement Heifers: Target Weights, Target Dates, and Fat Supplementation

1. Replacement Heifers: Target Weights, Target Dates, and Fat Supplementation Rick Funston and Gene Deutscher University of Nebraska

2. Feeding to a “Target Weight” % of Mature Wt @ breeding Item 55% 65% Pre-breeding wt 600 683 Conception (21d) 30 62 Calving wt. 834 897 Calf birth wt. 71 73 Calving difficulty,% 52 29 Calf death loss,% 6 5 Fall Preg Rate, % 85 93

3. Effect of Time of Gain From Weaning to Breeding on Heifer Performance No difference in age at puberty, conception rate, or calf performance the next year. Clanton et al., 1983 Percent of Target Gain EVENGAIN vs LATEGAIN, Age and Weight at Puberty, no effect, 12% less feed w/ LATEGAIN. Smith et al., 1995

4. What is the appropriate Target Weight??

5. Methods • 3-year study • MARC II heifers – 80 each year • Developed to either 55 or 60% of mature weight • Placed with bulls May 20 – 45 d • Data collected through 4th pregnancy diagnosis

6. Developing heifers to lower target weights

7. Developing heifers to lower target weights

8. Developing heifers to 53 vs 57% of mature weight: • Decreased costs $22/head • No differences in pregnancy rate • No differences in calf production • Decreased mature weight through 4th pregnancy diagnosis

9. Animals Must Fit The Environment !

10. When is the appropriate time to calve heifers for a June – calving cow herd???

11. Effect of Age and Time on Return to Estrus Age of CowDays after calving 40 50 60 70 80 90 100 % Cycling 5 or older 55 70 80 90 90 95 100 2-3 years 15 30 40 65 80 80 90

12. 18 16 14 12 10 CRUDEPROTEIN, % 8 6 4 2 0 APR MAY JUN JUL AUG SEP OCT NOV DEC FEB Crude Protein in Cattle Diets on Northern Great Plains Rangeland

13. Methods • 3-year study • MARC II heifers – 50 each year • Developed to reach 60% of mature weight at breeding • Placed with bulls either August or September 5th – 45 d • Data collected through 4th pregnancy diagnosis

14. Developing heifers to calve before or with the cow herd

15. Developing heifers to calve before or with the cow herd

16. Developing heifers to calve with the cow herd vs one-month earlier: • Decreased costs $11/head • No differences in pregnancy rate • Decreased calving difficulty • Decreased calf WW and adj 205 d weight • Tended to lower mature weight through 4th pregnancy diagnosis

17. Does Fat Supplementation Improve Reproductive Efficiency?

18. Introduction • Positive reproductive effects have been associated with fat supplementation independent of energy contribution • Increased pregnancy rates • Decreased duration of anestrus • Increased calf vigor

19. Heifer Development • Heifers that conceive early in the breeding season have a greater lifetime productivity (Lesmeister et al., 1973) • Fat supplemented heifers reached puberty earlier (diet X sire breed interaction) (Lammoglia et al., 2000) • Inconsistencies (Funston et al., 2000; Howlett et al., 2003)

20. Feeding 2 lb of whole sunflower seeds for either 30 or 60 d before PGF did not improve estrous response or pregnancy rate in beef heifers.

21. Linoleic Acid and Age at Puberty • Heifers fed whole sunflower seeds (5% added fat) from 4 months of age • CLA tissue content higher in HF • Leptin and insulin not different • IGF-I lower in HF group • Total cholesterol was increased in HF • No difference in age at puberty Garcia et al., 2003

22. Fat Source • In beef cattle, plant-derived fatty acids appear to have the greatest impact on reproductive performance (Burns and Filley, 2002) • Soybeans are readily available in Nebraska

23. Problems feeding whole soybeans? • Most research has been with pregnant beef cattle • Heifer development, MO, longer WSB were fed, lower the conception rates • Other negative effects reported by veterinarians • Why?

24. Soybean Phytoestrogen Analysis Phytoestrogen ppm Genistein 1095 Daidzein 940 Glycitein 100

25. Soybeans in Heifer Diets of Different Physiological Maturity

26. Objective 1) Investigate the inconsistencies associated with fat supplementation in heifers 2) Determine the effects of soybeans as the fat source in heifer diets of different physiological maturity

27. Experiment 1 Objective: • Determine how utilization of soybeans in heifer diets affect: • Cycling status • Synchronization rate • Conception rate • Pregnancy rate

28. Experiment 1 • 104 crossbred beef heifers • 660 lb • 10 months old • 3 lb whole soybeans • 4% added fat • Experimental period: 110 d

29. Heifer Diets

30. Methods • Synchronized estrus: • MGA (14 d) - PGF2a injection on d 110 (19 d later) • Artificially inseminated (AI): • 12 hours after visual detection of estrus • 1 of 2 randomly assigned sires

31. Methods • Bulls were placed with cows 10 days after last AI for 60-d breeding season • Pregnancy to AI determined by ultrasonography 45 d after last AI

32. Results • No differences in cycling status due to treatment: (P > 0.10)

33. Estrous Response Average Time d • Control 2.9 • WSB 3.2 P = 0.05 P < 0.05

34. Conception and Pregnancy Rates P > 0.10

35. Experiment 2 • Objective: Examine effects of fat supplementation (soybeans) on follicle characteristics of prepubertal heifers

36. Experiment 2 • 50 crossbred heifers • 470 lb, 9 mo. old • 3 lb soybeans + 1 lb corn • Control = 4 lb DDG • Experimental period = 161 d

37. Experiment 2 • Ultrasound guided follicular aspiration • 2 injections PGF2α 14 d apart • 60 h after 2nd injection (d 147) • Follicle Diameter • Aspirate • Placed with bulls for 45 d breeding season

39. Results • No differences in estrous activity due to treatment: • Sample period 1: 32% • Sample period 2: 84% (P > 0.10) • No difference in pregnancy rate (P > 0.10)

40. Experiment 2 • Aspirates will be assayed for: *Estrogen *Androstenedione (P = 0.166)

41. Experiment 3 • Objective: Examine effects of fat supplementation (soybeans) on follicle characteristics of postpubertal heifers

42. Experiment 3 • 20 crossbred virgin heifers • 780 lb • 3 lb Soybeans + 1 lb corn • Control: 4 lb Dried Distillers Grain • Experimental period: 30 d

43. Experiment 3 • Ultrasound guided follicular aspiration • 2 injections PGF2α 14 d apart • 60 h after 2nd injection • Follicle Diameter • Aspirate

44. Follicle Analysis • Aspirates will be assayed for: *Estrogen *Androstenedione (P < 0.07)

45. Supplementing Soybeans in Heifer Development Diets • Decreased synchronization rate • Increased time of synchronized estrous • No significant differences in AI conception or pregnancy rates, or final pregnancy rates • Follicular dynamics????

46. Heifer Development and Fat Supplementation • 548 lb, 9 mos; 24 per treatment • Fed diets for 113 d; (2% added fat) • Discontinued 1 week before MGA Howlett et al., 2003 (P > 0.10)