Every year, I receive calls from a few people looking to increase the nutrition and care of their beef bulls just prior to the breeding season in order to assure good fertility on pasture.
On each of these calls, I find it difficult to tell producers this type of attention should have already been done during wintertime. When bulls are finally released into the cowherd, it becomes a matter of managing supplements on pasture, watching their general well-being, and helping them cope with summertime heat-stress. Continuous bull management tends to keep the bulls in good shape, so as many cows and replacement heifers can be settled in a short breeding season, which contributes to ultimate financial success.
Once on pasture, one of the first rules of good breeding management dictates an acceptable stocking bull-to-cow ratio is chosen.
Calculating bull power
Although an exact bull/cow ratio depends on many factors (re: bull age, condition, libido, fertility, and breed); a good rule of thumb follows “one cow – per one month of age of the bull up to three years of age.” For example, a 20-month old bull could be run with 20 cows, while a three-year old bull could mate with 36 cows, respectively.
When grouping bulls in a multi-sire herd, it is a good idea to run bulls of similar ages, body size, and breed within the same cowherd group to minimize problems associated with fighting and individual bulls getting overused. For those operations that rotate bulls during the breeding season, older/experienced bulls should be use during the first part of the breeding season, followed up with the release of yearling bulls during the last few weeks. The idea is there is less breeding pressure upon young bulls because fewer open cows are available, which gives these yearlings more time to grow and mature.
The optimum stocking rates usually parallels my expectation active breeding bulls can lose between 100 to 150 kg of bodyweight. This loss equates to 0.5 to 2.0 units of body condition score, despite good quality pasture (TDN = 62 – 65 per cent, crude protein = 11 – 12 per cent) that should provide much of the essential energy and protein breeding bulls (and cows) require. If a bull gets too thin (re: BCS less than 2.0), I recommend it be pulled from pasture and substituted with a similar bull in better body condition.
Aside from providing good, quality pasture, I am a big advocate for providing a well-balanced mineral and vitamin program, which I believe is critical for maintaining good mineral status of breeding bulls (as well as cows). This contributes to good sperm production and libido. I recommend feeding a “breeder-type” loose mineral fed at three to four ounces, daily that contains complementary calcium and phosphorus levels to pasture grasses and has “chelated/organic” copper, manganese, zinc and selenium of high bio-available properties as well as high levels of A, D and E. In addition, make sure cattle have salt and a good source of clean water.
When putting out their minerals or other feed supplements, it is always a good idea to make daily observations about the general condition of each bull in the herd. I would watch for all types of physical problems ranging from eye injuries due to pinkeye to lameness caused by foot rot. On a rare occasion, I also have heard producers complain good bulls have broken their penis while breeding cows. Other producers have removed injured bulls due to fighting with other bulls.
Pay attention to heat stress
Aside from these concerns, heat-stress can be a big unseen problem, particularly for bulls released after the beginning of June. Temperatures above 27 C with at least 60 per cent humidity can literary sterilize bulls. Fortunately, this type of sterility is temporary (re: sperm production and recovery takes about 60 days), yet I have seen poor conception rates in a few cowherds traced back to otherwise fertile but heat-stressed bulls.
In one particular case, a producer showed me a 20-month-old bull that failed to breed a pot of 18 replacement heifers during a bout of 35 C weather, only to later successfully breed them in a fall-calving herd. It showed me that aside from providing trees for shade and a good source of water, there was really little the producer could do to combat severe bull suffering.
Regardless of heat-stress, producers are never entirely helpless, even if their breeding season falls upon the hottest months of the year. They can still implement an effective fly control program. I often recommend the strategic use of treated fly ear-tags approved in Canada, as well as dust bags, and back rubbers filled with insecticide located in loafing areas on pasture.