Focus on your yearlings this breeding season

Calving is well underway across the country and many of you are turning your thoughts to activities associated with breeding, pasture turnout and spring seeding. Before your schedule gets too hectic, it is a good time to take stock of your nutrition program particularly as it relates to the breeding herd. In past issues, I have focused on several occasions on pre- and postpartum nutrition of the mature beef cow stressing the importance of meeting her nutrient requirements for late gestation as well as lactation, particularly as it relates to getting her rebred early in the subsequent breeding season. While not downplaying the importance of this aspect of your nutrition program there are other animals in the herd that likely require even more attention than your mature cows. In this column I want to address some of the concerns we have with breeding replacement and first-calf heifers as well as with management of the yearling bull.

Developing replacement heifers is currently a hot topic in the research world. Traditionally the recommendation has been to grow replacement heifers to 60 to 65 per cent of mature body weight in order to ensure a majority has reached puberty by breeding and high pregnancy rates. Target gains typically are in the range of 0.7 to 0.9 kg per day which usually requires some form of supplemental feeding. Current research is challenging this dogma and is suggesting that replacements can be grown 55 per cent of mature body weight at breeding without any negative consequences on reproductive performance or lifetime productivity. Typically these programs are carried out under extensive, low-input systems. Heifers are grown out over the winter at low rates of gain and are expected to compensate with increased weight gains prior to, during and after the breeding season as they move onto spring grass and a higher plane of nutrition. This enhanced weight gain while on pasture is critical if these heifers are to catch up and reach 80 to 85 per cent of their mature body weight by calving. Whichever route you choose to develop your heifers, your concern at this time of the year is relatively simple. Are they on target, in appropriate condition and gaining appropriately as the breeding season approaches?

Most of you reading this column recognize that getting first-calf heifers rebred is a challenge. These animals have experienced all the physiological and nutritional stress of pregnancy, calving and lactation experienced by the older cows but are faced with the additional complication that they are still growing. These animals need to consume sufficient nutrients to meet all these needs if they are to be rebred early in the breeding season.

To give an example of the magnitude of these nutrient requirements consider a first-calf heifer weighing 1,100 pounds in the first month of lactation gaining one-half pound per day. This animal should consume about 24 pounds of dry matter (2.2 per cent of body weight) and according to Alberta Agriculture’s Cowbytes program, she requires 16 pounds of total digestible nutrients (TDN) and 2.5 pounds of crude protein per day or a diet concentration of 65 per cent TDN and 10.5 per cent crude protein. At this time of the year, the only way to ensure this level of nutrient intake is to feed a properly balanced ration or supplement these heifers on pasture. Failure to do so often results in heifers that catch late in the breeding season or in a high percentage of open heifers.

The final group that I want to focus on is the package of yearling bulls you recently purchased. As with your heifers these young growing animals require special attention if they are to be used successfully in the upcoming breeding season. Yearling bulls purchased from test stations or from purebred breeders likely need to be adjusted from relatively high-energy growing programs to forage-based rations. This diet change should be gradual in order not to throw them off feed. Yearling bulls should reach puberty two to four months prior to the date you expect to breed them and should be conditioned to your operation for a minimum of 60 days. Both steps help ensure that these young bulls will produce high-quality semen when turned out to breeding pasture.

During the conditioning period, keep in mind that yearlings are still growing. Target breeding weights should be a minimum of 55 per cent of mature weight. To meet this goal, your feeding program during conditioning will likely need to target two to 2.5 pounds a day gain. For a 1,300-pound bull, two pounds a day gain will require supplementing a good-quality alfalfa grass hay fed free choice with approximately five pounds of barley or its equivalent. A protein supplement may or may not be required, depending on the quality of the forage.

What do all these animals have in common? First, they are all young, actively growing animals that are the future foundation of your herd! Second, they are the most expensive animals you have ever brought into your herd. This is not the time to lose sight of the importance of their feeding program to their development as breeding animals.

About the author

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John McKinnon is a Professor Emeritus at the University of Saskatchewan and a consulting nutritionist who can be reached at [email protected].

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