Why Can Shortening Calving Interval Increase Production and Profitability? |
Gary N. Foster - CVNA Overview Profitability in a dairy herd is linked not only with cost of production but with production itself and the single most influential factor affecting daily bulk tank shipments, short of not feeding the cows, is breeding efficiency. If dairy cows produced milk on a flat line, that is if all throughout her lactation a cow produced 60 lbs of milk day-in and day-out from the time she freshened until the day she was dried, breeding efficiency would be irrelevant to production. The interval between calves would be meaningless except in terms of the heifer replacement program. However, since her production can vary from 100+ lbs of milk at peak production in the 30-60 DIM range to 40 to 50 lbs or less at the "tail end" of the lactation, breeding efficiency, calving interval and DIM combine to create a major impact on daily bulk tank shipments. Indeed, calving interval and DIM are a function of breeding efficiency. A Single Cow Perhaps the simplest way to illustrate this phenomenon is to use the example of a single cow. If there was only one cow milking into the bulk tank every day, in the early stages of her lactation production would be "up", that is around 12 gallons of milk or so daily. In the late stages of lactation production would be "down" around 5 gallons. If she were in mid lactation we would expect approximately 8 gallons per head per day. Obviously, this is not flat line production but rather production on a curve that peaks 30-60 DIM and concludes somewhere around 275 days later, dropping after peak about 10% each month from the previous month's production until the cow is dried off. In the example of a single cow the impact of DIM on production becomes very clear - the earlier she is in lactation - to a point - the more milk there is to ship. Conversely, the later she is in lactation the less milk there is to ship. What is True of One is True of All In a dairy herd, obviously, there are many cows milking simultaneously and in varying stages of lactation. However, the same DIM figure that tells us what kind of production we can expect from a single cow - when it becomes AVERAGE DIM for the entire herd - can also tell us what kind of production to expect from a group of cows. As an example, a herd of 850 cows with a good production curve and with all cows in early lactation (60 DIM average), will produce approximately 850 X 12gal = 10200 gallons of milk daily. This same group of cows in late lactation, around 335 DIM will produce about 850 X 5gal = 4250 gallons of milk daily. Of course, in mid lactation at about 168 DIM average they would produce about 6800 gallons daily(1). Obviously, if we could maintain this 850 cow herd at a constant 60 DIM figure, we could ship 10200 gallons of milk every day of the year. However, mother nature imposes a few significant limitations on that very profitable prospect.
Consequently, the best we can hope to do is to get her back on her feed and into early lactation production AS SOON AS WE CAN SAFELY DO SO. Breeding Efficiency - Calving - DIM - Milk Flow This is where things become a bit complicated because we can't get her back into early lactation production until she calves again. However, if we haven't managed to detect her heats efficiently during the PREVIOUS lactation and get her bred so that she has conceived in 115 days or less then we will be forced to milk her at a lower production level with a smaller net return over feed cost until she can be dried off and subsequently calve again. Worse yet, it for some reason, nutritional or otherwise, she wasn't cycling early enough or didn't settle when bred a couple of times we enter a PROTRACTED period in late lactation in which we are forced to feed her at a break even position or below. This situation becomes even more dismal if it is a HERD TREND because calving interval - the time between calves - has a direct effect upon the average DIM of the herd and as we have seen, DIM has a direct and profound impact on daily bulk tank shipments. As an example, if this herd of 850 cows freshened in a pattern that yielded the same percentage of fresh cows per month over a given calving interval, it would then be possible to figure average DIM based on calving interval. Since the calving figure includes dry time, the first thing we do is subtract the dry time from the calving interval. This gives us an average LENGTH of lactation. In our example we will use 2 months as the dry time - Calving interval 13 months - 2 months dry time = 11 months as the average LENGTH of lactation. The average number of days in the lactation = 11 months * 30.5 (avg. days in a month) or 335.5 days. Since this herd has an EVEN CALVING PATTERN with the same number of animals freshening each month the average DIM would be exactly one half of the length of the lactation or 335.5 * .5 or 168 DIM. Contrast this with the average DIM of a 14.2 month calving interval 14.2 months - 2 months dry time = 12.2 months * 30.5 days = 372.1 days * .5 = 186 DIM. Only Eighteen Days-In-Milk A mere 18 DIM difference? What appears to be mere actually adds up to be MUCH. Let's take our mid lactation production figure of 8 gallons or 68.8 lbs of milk at 168 DIM and calculate the effect on daily bulk tank shipments of shifting average DIM from 168 to 186. Production decline after peak on a whole herd lactation curve is approximately 10% per month. That means that moving from 168 DIM to 198 DIM - or 30 days would reduce daily milk by 6.9 lbs. per head per day. If that is the case then moving from 168 DIM to 186 DIM - an 18 day shift - would decrease average daily milk by 59% of that figure (18/30.5=59%) or 4.07 lbs of milk or about one half gallon per head per day dropping the average daily milk per head per day the 8 gallon figure to 7.5 gallons. Consider the impact this decline in average daily production has on monthly milk income. Daily milk shipments would drop from 6800 gallons to 6375 gallons daily (850 cows * .5 gallon = 425 gallons lost production). This drop in daily milk shipments will reduce monthly income by over $11,000.00 per month (425 gallons * $.90 = $382.50 * 30.5 days = $11,666.25) Now let's look at the other side of the coin. If an extended calving interval is the result of a combination of missed heats, improper semen handling and/or A. I. technique etc., and not nutritional or production stress factors, DECREASING calving interval resulting in a DECREASE in average DIM of a "mere" 18 days will INCREASE average daily production by 1/2 gallon of milk per head per day WITHOUT altering the basic feeding program. Feed costs per head per day at any given level of production will remain constant and RETURN OVER FEED COST will increase significantly. Summary In summary then, just as a single cow gives more milk in early lactation than she does in mid or late lactation, an entire herd produces more milk as the average DIM of the herd decreases. Consequently, employing good herd health practices after calving, effective heat detection, proper semen handling and effective A. I. technique etc. to shorten a calving interval from 14.2 months to 13.0 months can increase average daily milk production by 1/2 gallon per head per day. The increase in production and profitability results from shortening calving interval which moves the herd average DIM toward early lactation production rather than away from it. Early lactation production is the greatest, most efficient and most profitable production of the entire lactation. Footnotes (1). These production figures are based on an assumed production curve. Obviously, changes in the shape and dimension of the curve itself will also affect daily bulk tank shipments. As milk production becomes more persistent after peak with the use of bST and other ermerging technologies, longer calving intervals may become more profitable as well as more necessary. As the production curve moves more toward the shape of a flat line, the importance of calving interval to consistently high milk flow diminishes correspondingly. |