Our maxim at Te Mooi Speckle Park is “Better Beef, Bigger Profits”. The key to bigger profits in a commercial beef enterprise is fertility. More calves on the ground mean more kilograms of beef produced. Calves born earlier in the season wean heavier, and improved fertility can also contribute to reduced labour cost through the shortening of the calving period.
The real measure of fertility is days to calving as it brings together all the factors that contribute to the successful production of a calf every year in a timely fashion. This is, when it’s all said and done, the most crucial function of every cow.
The four Australian Angus Selection Indexes are made up of 14 EBV traits that are given different weightings based on their relative importance to profit. Days to Calving carries the heaviest weighting in two of the four indexes, placing second and fourth in the other two. It is of great significance to the bottom line of a beef production system.
Days to calving can be split into three phases. Gestation length, postpartum anestrous (the time to first estrous post-calving), and time from first estrous to conception. The ideal is for a cow to maintain a 365 day of shorter time between calvings. Gestation is the bulk of this period. Gestation length ranges from about 275 to 290 days and can be selected for and reduced to a point, but a gestation length of 275 to 277 seems to be the optimum for reduction in dystocia and maintaining calf vitality.
“Optimal gestation length was determined in the range of 275 - 277 days based on calving ease and stillbirth rates.”
Zenon Nogalski and Dariusz Piwczyński
Asian-Australas Journal Animal Science
Postpartum anestrous last 60 to 90 days in mature cows and 90 to 120 days in heifers and is highly affected by the body condition of the individual, as seen in the graph below from Virginia Tech. Adequate body condition can reduce postpartum anestrous by more than 30 days. A female's ability to maintain condition is crucial. It not only helps her stay in the calving pattern, but also enables her to calve earlier in the calving period, allowing more time for growth for the calf prior to sale, and as they say in the classics, and it was never more true than with livestock “time is money”. At a growth rate of 0.8 kilograms per day and at a price of $3.30 per kilogram the advantage of calving 30 days earlier equates to a premium of nearly $80 per head.
“Prolonged postpartum anestrus is a main factor limiting reproductive efficiency in cattle”
Montiel F, Ahuja C.
Animal Reproductive Science 2005
Source: Virginia Cooperative Extension, Virginia Tech
Highly fertile herds should have a 70% pregnancy rate per cycle enabling 93% pregnancy with a two-cycle, six-week joining period. Selecting females that conceive early has a low, but positive heritability. It is a slow road to hoe and management can play a much bigger role than genetics in this area as condition score and energy intake are critical to fertility rates. The days to calving EBV has a significant impact on profitability and There is also evidence that using this EBV as a selection tool can impact on sexual maturity and precocity.
“The genetic correlation estimates indicate that the use of DC (Days to Calving) in the selection of beef cattle may promote favorable correlated responses to age at first mating and, consequently, higher gains in sexual precocity can be expected.”
For the good of the breed, Speckle Park breeders should be contributing the data required to allow a Days To Calving EBV to be produced. In order for days to calving to be analysed producers must submit the joining details of naturally mated females, information on females removed from the herd, and all birth dates of their calves. This information is very valuable and easy to collect and contribute. It is a path to improved profitability.
Research undertaken by the CRC with Brahman herds have shown that selecting bulls with superior genetics for reproductive traits, such as Days to Calving, results in significant economic gains. One astonishing bull in the project reduced the days to calving of his daughters by more than two weeks. This reduction in days to calving resulted in a increased calving rate of 15%.
In further research done by the Northern Territory Department of Resources, also in Brahman cattle, showed that selecting for fertility traits increased yearling heifer conception rates by 35% and lactating cow re-conception rates by 31%. Selection on fertility traits can result in significant improvements in herd fertility and overall profitability.
“Note that there is only a small favourable relationship between SS and DC. Therefore it is strongly recommended that you select for the DC trait directly if you want to improve female fertility.”
Many of us assume that selecting for scrotal size will improve female fertility and reduce the age of sexual maturity. Furture Beef however report that there is only a small impact of scrotal size on female fertility, and this is backed up by an article published in the Journal Of Animal Science in 2003. Their conclusion following a study of thirteen Bos Taurus breeds is summed up in the quote below.
“These results suggest that genetic response in female reproductive traits through sire selection on yearling SC is not expected to be effective.”
Martínez-Velázquez G, Gregory KE, Bennett GL, Van Vleck LD
Journal of Animal Science, 2003
You may well disagree with their findings as the prevailing opinion is that scrotal size is strongly linked to female fertility. Even if you do disagree, we should all be contributing the information required to establish a Days to calving EBV, as it is proven to improve fertility and profitability, which can only benefit the breed.