Table 1. Economic Comparison of Conception to Weaning Efficiencies. (Based on a Herd of 100 Head) Conception to Weaning Percentage                           85                           90                         95         Total Added Cost                                                   $4500.00                  $3000.00             $1500.00 Production Cost per Prod. Animal                          $52.94                      $33.33                 $15.78 Total Lost Sales Revenue                                     $9375.00                 $6250.00             $3125.00 Total Losses                                                         $13,875.00                 $9250.00             $4625.00

As you can see the losses are reduced dramatically when reproductive efficiency improves. A 10 percent improvement in calving percentage will result in a 66.67 percent reduction in total revenue losses for a 100 head breeding operation based on these assumed values. If total productioin cycle per animal unit lost is $925.00 ($300 + $625) over 15 months then annual losses are equal to $740 ($925/15 * 12 months). Thus it becomes obvious that it is cost effective to take steps to improve reproductive performance.

Strategies to Enhance Reproduction

While many techniques are available that can manipulate reproduction (heat synchronization, A. I., ET) most of the opportunities to enhance reproduction are nutritionally related. Let's take a look at a number of these:

1) Bull Management – managing bulls on many operations seems to be an afterthought. Many commercial producers seem to believe that as long as they have some sort of male bovine out in the pasture with their females, they have it covered. This could not be farther from the truth. Remember that your bull is ½ of each calf and that it takes a fully functional bull to get cows bred in an appropriate period of time. Additionally, since one bull can sire 10 to 40 calves (limited breeding season. One bull can handle more if allowed access to the herd for longer periods of time), he has a profound effect on the breeding efficiency and, as importantly, profitability of the herd. For instance, if a commercial producer does his homework and carefully selects a bull to enhance his calves weaning weights he might realize significant increases in these weights. In this situation, he might increase his weaning weights by 50 lbs per head. Using the $1.25 figure from above this means that each calf is worth $62.50 per head more than the previous year with a lesser bull. This means if he gets 40 head bred the additional revenues generated would equal $2,500.00. If this bull is carefully managed bis productive life could be 5-8 years. With an average productive life of 6.5 years this would meant that this bull could generate an additional $16,250 over his lifetime. Thus selection of genetically superior animals that may cost more ($3,000-$4,000 per head) makes economic sense as compared to buying a bargain basement special for $1000 at the auction ring.

As mentioned, bulls need to be cared for properly, paying attention to their health and nutrition. Body condition is as important in bulls as it is in cows and thus, bulls need to be properly conditioned (but not excessively fat) when they are put with the cows for the breeding season. Aggressive bulls will forgo eating in many cases to pursue breeding activities meaning that nutrient intake is down and that they will loose weight as the breeding season proceeds. They need to be in adequate condition going in so that they can breed as effectively toward the end of the season as they do at the beginning.

Bulls should also be fertility tested by your veterinarian prior to the breeding season. There is nothing worse than placing a bull who is infertile with a group of cows only to wonder why, 2/3 of the way through the breeding season, all the cows in a given group still seem to be cycling. A simple trip to the vet can confirm that your bull(s) are sound and is very cheap insurance.

2) Use of Ionophores. Funston (2006), in a paper given at the Applied Reproductive Strategies in Beef Cattle Conference, reported that the use of ionophores (RumensinTM and BovatecTM) have been shown to influence reproductive performance during the postpartum period. Remember that ionophores are a feed additive that improves feed efficiency and gains (by changing rumen fermentation patterns), thus they allow for improved energy utilization by the animal from feeds and forages. Cows and heifers fed an ionophore exhibit a shorter post partum interval (shorter time between calving and rebreeding) provided adequate energy is supplied in the diet (Table 2, Randel, 1990). This effect appears to be more evident in less intensely managed herds that generally have a moderate (60 to 85 days) or longer postpartum interval. This simply means that if you already have a reasonably short PPI (i.e. 30 to 60 days) you may not see as much of an effect. Researchers have also shown that heifers fed an ionophore reach puberty at an earlier age and a lighter weight.

Table 2. Effect of Ionophore Feeding on Postpartum Interval (PPI) in Beef Cows and Heifers                 Study                       Ionophore                      Control                           Difference                                      (PPI, days)                    (PPI, days)                          (days) ________________________________________________________________________________                1                                 30                                   42                                      -12                    2                                 59                                   69                                      -10                    3                                 67                                   72                                        -5                    4                                 65                                   86                                      -21                    5                                 92                                 138                                      -46

3) Fat Supplementation. A great deal of work has been conducted over the last few years on the effects of feeding fat to enhance reproductive performance. It is well known that inadequate energy intake and poor body condition can and does negatively effect reproductive function. Supplementation of fats has been used to increase the energy density of the cows diet in general and avoid undesirable, negative associative effects that are sometimes seen when high grain supplements are used in conjunction with a forage or roughage based program.

Supplemental fats may also have positive effects not associated with energy contribution. Dietary fats have been shown to positively affect reproductive function by roles played at the hypothalamus, pituitary, ovary and uterus, i.e. primary sights of hormone production. This appears to be related to the type of fatty acids making up the dietary fat (remember that overall dietary fats are made up of smaller units called fatty acids just as proteins are made up of smaller units called amino acids).

The use of supplemental fats has been investigated at a variety of production stages and a variety of responses have been noted. Consider the following:

a) Fat Supplementation to Replacement Heifers – Studies in this area are, in fact, somewhat limited. Fat supplementation appears to have a positive on breeding of heifers when they have been nutritionally challenged. Well developed heifers and those on a suitable plane of nutrition have shown limited responses to feeding of fats

b) Fat Supplementation Prepartum (Prior to calving) – A study by Hess in 2003 summarized research on supplementing fat during late gestation and concluded that feeding fat to beef cows for about 60 days prior to calving resulted in a 6.4 percent improvement in pregnancy rate for the upcoming breeding season.

c) Fat Supplementation Postpartum (after calving) – Studies have shown an increase in reproductive response when feeding increased dietary fats to cows post calving. One particular study conducted in South Texas showed an increase in breeding rates in thin cows (BCS ~ 3.5 to 4) when cows were supplemented with 3 to 4 lbs of whole cottonseed per head per day.

Fat supplementation, however, may not be the answer to cow/calf producers breeding woes. Some research has shown both increases and decreases in the production of PGF2x, an important reproductive hormone. In some situations where higher fat levels are fed for an extended period of time, PGF2x synthesis is increased and this may compromise early embryo survival. As with all production components, moderation and care in use are important. A producer cannot assume that one practice will solve all his problems or that “if a little is good, a lot must be better!”

Conclusions

Breeding management is probably one of the cow/calf producer's most important jobs. Adhering to the basics and utilization of enhancement techniques can prove profitable to his operation. In the next part of this series we will look at additional opportunities a producer can utilize to improve his breeding performance.

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, Texas. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at 903-885-7992 or by e-mail at sblez@hughes.net.