FERTILITY

As I work with beef herds, a glaring problem on many herds is inadequate herd fertility. This is expressed as one or more of the following:

• too many open cows
• too many late calvers
• extended calving season

All these problems lead to a weakening of the beef business.

How do we investigate this problem and how do we solve the problem? The common problems I find are:

• replacement heifer selection is substandard (too big, wrong genetics, no heterosis)
• inadequate heifer development (primarily nutrition concerns)
• wrong genetics for the environment and management (don't want 1600 pound, high maintenance cows)
• blaming diseases for management issues

History and Physical Exam

We begin by taking an excellent herd history and then doing a thorough physical examination of the entire enterprise (no different than on a single sick animal). We use a methodical system so as not to miss an important point.

Replacement Heifers

The easiest and many times most logical place to start when we have inadequate fertility is with the potential replacement heifers. These animals represent the future of the herd. If it is prebreeding, we need to schedule time to:

• reproductive tract score (RTS)
• yearling weight
• frame score
• disposition score
• +/- pelvic measure
• vaccinate
• buying expensive mineral mixes to solve management issues

This is a plan using the "system's concept" where we package a number of procedures as a unit. This is our "heifer prebreeding examination".

On our RTS we want to keep the heifers rating 4 & 5. If many are 3 you may have time to feed them to get them cycling. This depends on many factors. Generally, the 1 and 2 heifers should be implanted and eased onto a finishing ration and then sold for slaughter.

The prebreeding weight should be 55-65% of mature weight at breeding. (Newer research by Deutscher et. al. in Nebraska shows 55% may be adequate in spring born heifers.)

For frame score, we generally want heifers about FS 4.0-6.0. The following table gives approximate mature weights. (Don't confuse frame score with body condition score (BCS) which is a measure of fatness.)

If nutrition is marginal, we need frame score 4-5 cows so we can have adequate herd fertility. If resources are excellent and larger cows can be economically kept, a frame score 6 cow may be fine. Each farm may be quite different. The above chart is for cows in Body Condition Score 5.

Now we have heifers that are ready to breed. With improving fertility as a goal, we need to have a short breeding period for heifers. I strongly suggest 30-42 days. Think through the "big picture". If you have many potential replacements and want to be really selective on calving time, breed for only 30 days. If nutrition is excellent and we have only 10-20% more heifers available than we need to have bred, go with 42 days. Whatever choice, it needs to be shorter than the cow breeding season. This is a very important factor for success!

Synchronization for AI

The MGA-prostaglandin system is the gold standard for heifers. MGA Select Synch is another possibility. You can view and print our MGA-prostaglandin client handout. You can find a spreadsheet program ($25) for each synchronization program at www.ibc.iastate.edu

Bull Breeding

If the owner is not set-up to AI, I still like to feed MGA for 14 days and then turn the bull in 17 days later (no prostaglandin injection). You need adequate bull power if you do this. You wouldn't want to do this with a yearling bull and 20 heifers.

In a total bull bred herd, I figure the cows:bull ratio at 1 cow for every month of age of the bull. So, if the bull is 15 months of age, he can service 15 cows in a 65 day breeding season. This ratio works from 15 - 50 months of age. Obviously, a 10 year old bull (120 months) could not handle 120 cows! This is only a rule of thumb and you should know that some breeds are higher infertility than others. Also, composite or hybrid bulls will be able to service more cows than a purebred. I figure the hybrid advantage at 10-20%.

When to Calve

It is ideal to calve heifers 14-21 days before the cow herd. Why?

• disease reasons - "clean environment"
• time reasons - more likely to check 3-4x daily early in season
• fertility reasons - extra 14-21 days to regain weight for upcoming cow 65 day breeding season

Example: See "Breeding heifers before cows"

Why breed for only 30-42 days?

Early calving heifers have a much greater chance of rebreeding on time (more time between calving and rebreeding). A late calving heifer becomes a late calving cow or an open cow. Neither of these options is acceptable.

If I ranked all the deficiencies of all the herds where I've consulted, fertility problems would be very high. Getting a "buy in" of the early and short season for heifers will be a major step in the right direction.

Cow Herd

The goal in most areas is to have a 65 day breeding season where the following percentages achieved:

In an ideal herd, 50% of the calves have been born by day 17 of the calving season. This is absolutely achievable.

Why only 65 days?

It costs no more to feed a cow that calves March 1 vs. one that calves June 10. That 100 day advantage will produce an extra 200-250 lb. at weaning. At today's prices the advantage would amount to about $250-350 extra income.

Why not less than 65 days?

If you look at the % calves born/21 days, we quickly see that if we drop to a 42 day breeding season for the cows, we would likely only get an 88% calf crop. A 12% open rate is unacceptable in all but the harshest of environments. If we have 100 cows all in heat on day one of the breeding season and have adequate bull power via natural services or AI, we'll likely only get 65-75% of these cows pregnant. Approximately 21 days later we'll have those 25-35 cows that did not settle for whatever reason again showing heat. If we again get 65-75% of these bred, we still have about 10-12 open cows after two cycles. We need that third cycle to get up to our goal of 95% bred in 65 days.

Fertility and Profitability

Cowherd fertility is the number two factor in herd profitability with herd feed cost being first. It is obvious that if you don't feed the cows properly, you won't have an acceptable pregnancy rate. But paradoxically we also don't want a 100% pregnancy rate year after year as these herds are almost surely spending too much on nutrition. We actually expect some level of open cows each year because we know there will be cows that for a number of reasons do not become pregnant in our defined breeding season. Herds with fertility problems are generally either under feeding their cows or have cows that simply do not fit their environment.

Goals

You need to set goals for your producers as to Body Condition Score (BCS) at calving. Here are the guidelines:

*Heifers of average-high milk production potential need to be in higher BCS than low milk potential heifers. Much of the literature suggests BCS 6 which is fine for low milk potential heifers, but is inadequate for heifers with high milk potential (1º Simmental or Gelbvieh cross).

Nutritional requirements - cows

*based on March 1 calving date

You will note that a cow's energy needs increase by 30% and protein needs increase by 40% post-calving. Ease the cows onto this ration close to calving.

Also, note that there is only one way to decrease a cow's energy need by 23% and her protein need by 36% from period 2 to 3. Wean the calf! Weaning the calf at approximately 160-200 days is a huge benefit to herds with fertility problems. This allows:

1. the cow to go into winter in better flesh
2. the cow to utilize low cost crop residues or stock-piled grass for winter feeding
3. the calf to be fed directly instead of feeding the cow to feed the calf - much more efficient

Miscellaneous Fertility Problems

1. Infertile bull - can be a major disaster. Bulls need a Breeding Soundness Examination every year (do at same time as heifer prebreeding program).
2. Bulls with lack of effective libido - much more infrequent problem. Always watch bulls for activity early in breeding season.
3. Use of MLV IBR (injectable) vaccine in seronegative females within 21 days of breeding. Our recommendation is to vaccinate cows and heifers at least 30 days prebreeding.
4. Feeding MGA for extended times. MGA feeding should be for only 14 days. Longer periods can cause reduced fertility.
5. Retained placenta - generally not a real problem in beef.
   1. 98%+ need no treatment
   2. uterus will expel infection as cow comes to estrus
   3. can give PGF2 about 30 days postpartum
   4. <2% of cows need systemic Rx. (Penicillin SID for 3 days)

The "Big Two" Fertility Problems

1. Extended calving season
2. Anestrus in nursing first calf heifers

A. Extended calving season

I call anything over 65 days an extended calving season for cows. Generally I consider herds as a problem when they are over 90 days. This is arbitrary and just my number. If I have a herd that has a 60% dystocia rate in heifers and a 15% death loss preweaning, I'm not going to jump on a 100 day calving season. We always begin herd improvement with the "weakest link in the chain".

If a herd has an extended calving season (we'll pick 150 days), we need to attack the problem from two directions.

1. Breed heifers before cows AND for only 30-42 days
2. Cut 30-40 days off the length of the breeding season each year for 3 years. Each year pull the bulls 30-40 days earlier than the year before.

Also, I suggest improving energy intake of cows precalving and this will "move up" many of the late-calvers.

For this to truly work, you cannot have a "favorite" cow. If this is the case, give her a name and she officially becomes a pet!

B. Anestrus in nursing two year-olds

By far the most important factor in improving second calf heifer fertility is to have two-year old heifers in BCS 6 ½-7 at calving. I cannot overemphasize this point. If you don't have 80% of your nursing two-year-old (synonym is "first calf heifer") cycling by 60 days postpartum, your precalving nutrition was inadequate.

The second critical factor for getting heifers to cycle is having them separate from cows precalving through breeding. The aggressive behavior of the cows is a real negative for these young, naive heifers. When fed as a group, the heifers very rarely get their fair share of feed. Bred heifers also need increased levels of protein and energy compared to the cows. Bred heifers are still growing, so calories are going to:

• maintenance
• fetal growth
• colostrum/milk formation
• heifer growth

Cows have only the first three requirements.

It has been my experience that the "separate due to nutritional differences" argument has not been totally effective in invoking a change in management. When we reinforce the "disease argument", then a change is generally made. We know that when cows and heifers calve in the same environment we will increase sickness by three times in our calves compared to having them separate. This is a valid point and one that should pique your interest.

Other causes of anestrus in first calf heifers:

• inadequate post-calving nutrition - heifers need a similar increase in protein and energy postpartum as cows
• problems with disease (metritis, parasitism, etc.) causing anestrus are uncommon
• dystocia has a negative correlation with subsequent fertility in these heifers

FAQ from Clients

1. What about dystocia problems in heifers calving in BCS 6 ½-7?

Taking heifers from BCS 4 to 6 will increase birth weight 0-7 pounds (depending on study) but all reports show no difference in dystocia score. This fallacy of feeding heifers a little grain precalving and causing monumental calving difficulties needs to be killed and buried. Just look at the above chart. We saw a light increase in birth weight and NO DIFFERENCE in percentage of heifers needing calving assistance!! But, look at the tremendous response to fertility. The heifers in BCS 4 had only 56% bred back to calve the next year while the heifers in BCS 6 had 96% bred back.

2. What about calving heifers in BCS lesser than 6 and then feeding a higher energy diet?

If heifers are near BCS 6, this will likely work, but if heifers are BCS 5 or lower, the heifer will likely use the increased energy for additional milk production and not gain enough weight to begin cycling.

Other Tips to Improve Fertility

1. Feeding whole soybeans

• Research from Missouri (2001) shows that feeding 3½ lb. whole soybeans/cow/day (3#/head/day for heifers) for 30 days before the start of the calving season improved first service conception rate from 63% to 87%.

2. Twice daily nursing

• a small trial we did in Iowa on some late-calving cows produced the following results


• average days from start of trial to estrus = 13 days
• average days post-calving to estrus = 47 days
• average days "moved up" in calving interval = 36 days


• works well on thin cows and heifers

3. 48 hour calf removal

• Expect about 8% more cows to cycle in a synchronized estrus if you use calf removal. This works best if cows are less likely to cycle (thin, short PPI). I think of this as a one time fix and not a long-term solution.

4. Bull exposure

• Having a herd bull (or "teaser bull") in with cows at calving will stimulate an earlier estrus in cows. The average would be about 21 days. This is a great technique for late-calvers. Put the bull in with them even before they calve.

5. Steer calves

Heifers nursing steer calves showed estrus 6-7 days before cows nursing bull calves. So, in commercial herds, this is another benefit of early castration.