Late lactation is an important, yet often overlooked part of the lactation cycle. It’s easy to let cows coast to the finish line, getting fat and lazy along the way.
While it’s inevitable cows will gain weight as they get closer to their dry period, it’s important to make sure cows are not adding body condition to the point where they will be overconditioned. This sets them up for calving and metabolic problems that negatively impact reproductive success and milk production potential in the next lactation. Maintaining milk production persistency will help prevent cows from becoming overly fat.
Gabriella Varga from Penn State University tells producers she would rather have a milky-looking cow at calving than a cow with excessive fat cover. Varga recommends producers set a goal to have cows average a body condition score (BCS) of 3.25 at calving. A body condition score of 3.5 is acceptable, but avoid having cows with scores any higher than that at calving. Varga points to studies done at Cornell and Penn State that show cows freshening with a BCS higher than 3.5 will lose about 5 pounds of milk per day during the first 30 days in lactation.
Avoid the vicious circle
Anything done in late lactation to prevent overconditioning will translate into four things:
• Less body condition loss at calving
• Fewer metabolic problems such as ketosis, fatty liver and displaced abomasums
• Better reproductive results in the next lactation
• More production
Cows that freshen overweight will lose one body condition score in 30 days. Because this is a slow process, fat cows will spend more time in a negative energy balance, resulting in metabolic disorders and reproductive problems. Overconditioned cows are more likely to experience ketosis, fatty liver and displaced abomasums after calving.
Cows in a negative energy balance are not ready to become pregnant, and often those that become pregnant can’t maintain embryos, says Varga. That leads to a vicious cycle of more breeding attempts, longer days in milk, calving problems and additional health issues during future lactations.
Varga recommends cows be bred back early in lactation so they are not milking for longer than 315 days. She also urges producers to keep the dry period short to avoid overconditioning. If these guidelines are not followed, lower production may result.
Improve milk persistency
Proper ration balancing and maintaining production consistency are two areas dairy producers can address to improve profitability in their late-lactation pen. One way to maintain milk persistency is through the use of bovine somatotropin (bST), which can enhance production and keep cows from putting on extra weight. A single total mixed ration (TMR) can be fed safely because production makes a slower decline in later lactation. This has worked well to simplify feed management and keep producers who are not willing to give up feeding one ration happy. Keep in mind, though, that feed costs will increase because cows administered bST will consume more dry matter.
Recently, many cooperatives have banned the use of bST, making this technology and management tool unavailable. In that case, a late-lactation ration should be balanced to prevent the increased body condition that can result if these cows are fed diets formulated for high-producing cows.
Adjust the ration for late lactation
Dairy producers and nutritionists can still push late-lactation cows by formulating a ration designed specifically for this group, says Varga. The best way for this to be done is to separate low-producing cows so they can be fed a low-energy ration specifically balanced for their needs. For producers who feed one TMR this method can still work, says Varga. Managers can mix one ration, but feed less to the separate pen of late-lactation cows.
For example, if you are feeding 50 pounds of dry matter (DM) to the high-producing group, cutting the low-group ration down to 45 pounds can be a better financial investment. You must, however, be certain sufficient bunk space is available to prevent dominant cows from eating to capacity while other cows receive less than the desired amount of feed per day.
Another way to make this group of cows more profitable is to feed a ration balanced for amino acids and containing a rumen-bypass methionine source. These diets are predominantly lower in crude protein, which allows producers to spend less on protein supplements. Also, cows can better utilize nitrogen to keep it from entering the environment, leading to feed efficiency or more milk and components per pound of feed. Milk with higher milk fat and protein levels results in a larger milk check as well. Until now, some suggest dairy producers have overfed protein to cows in late lactation, supplying the requisite amino acids at the expense of oversupplying all amino acids. With a current focus on reducing nitrogen excretion and high feed prices this practice becomes less attractive. Reducing dietary protein but still balancing for amino acids allows for reduced nitrogen excretion while maintaining milk and component production, creating increased efficiency.
Keep rations consistent in late lactation
Cows in general like to do the same thing day after day, and cows in late lactation are no exception. Honing the ration to make certain there are no abrupt changes or wide variations in the nutrients from day-to-day is critical. Just as early- lactation and high-producing cows need a properly functioning rumen to reach and maintain peak milk, late-lactation cows need the same consistency toward the end of their lactations to maintain persistent milk and component production. Maintaining persistency of production in the latter stages of lactation can be achieved one of two ways:
• The wrong way is to sacrifice high peak milk and then maintain the lower peak through the end of lactation. This is neither economically sound, nor profitable.
• The correct way is to achieve high peaks and then try to maintain them through the lactation.
A major hurdle with later-lactation feeding is the move from high- to low-energy rations. At this time, many cows will produce less milk because that is what they are being fed for. One of the hardest concepts is feeding for the amount of milk a cow should be making rather than formulating the ration for her current production. It’s difficult because ration costs may escalate, but if fed for her current production, it is likely her output will continue to decline even more. With increased feed, persistency in late lactation can be achieved.
As the lactation goes on, feed efficiencies continue to decrease. Boosting feeding efficiencies in the ration is another option that can prove beneficial – both for your cows and your wallet. Nutritionally, there are three basic areas on which to focus attention:
• Rumen function – Feed ingredients that promote rumen microbial growth and increase microbial proteins. This can lead to improved milk and protein production. Increased high-quality microbial protein is linked to improved dry matter intake (DMI) and increased milk production, which are as important for late-lactation cows as for early-lactation cows.
• Amino acids – Methionine is often the first- or second-limiting nutrient in the diets of high-producing dairy cows. Since it’s essential to the synthesis of milk protein, limited methionine levels cause reduced milk and milk protein production. A rumen-protected methionine source bypasses the rumen and is absorbed in the cow’s small intestine to be used by the mammary cells to synthesize milk protein, especially if dietary protein is not being fed in excess of requirements.
• Monitor DCAD levels – Maintaining a positive dietary cation-anion difference (DCAD) during lactation increases blood buffering capacity and creates a more stable environment inside the cow. The result is improved DMI and, ultimately, higher milk and component production during a cow’s entire lactation. Feeding to achieve DCAD levels of +35 to +45 meq per 100 grams of DM has shown to be the most beneficial for milking cows in early lactation. For cows in later lactation, literature suggests a DCAD of +25 to +30 is optimal.
Beyond the ration, following herd health protocols can be a major player in persistency. Once a cow is sick, has a bad case of mastitis or experiences extreme heat stress, it’s almost impossible to get milk production back to where it once was. Implementing and following herd health protocols can improve persistency. If you have had underfed animals or high incidence of heat stress, there is hope. Researchers have found it may take some time for cows to improve, some as long as four to six weeks, before you will see any differences, but production can return to high levels.
Keeping late-lactation cows producing high volumes of milk is a challenge. Although it would be much easier to forget about this group, paying a little more attention to herd grouping, ration changes and feed ingredients can really pay off financially. PD
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