Heat stress takes its toll on your herd in several ways.

With heat stress season right around the corner, I was fortunate to be included in discussions last week with Dr. Robert Collier of the University of Arizona.

Dr. Collier and his colleagues (including Dr. John Smith, who passed away in March) have been at the forefront of heat stress research in dairy cattle.

Here are some bullet points from my notes:

• Heat stress begins to affect dairy cows producing more than about 75 lb. of milk at a temperature humidity index (THI) over 68. (THI table below). Death rate increases when the minimum THI during the day is 70 and the maximum THI is 80 or higher.

• Respiratory rates over 60 breaths/minute indicate heat stress in cows.

• Hot cows don’t lie down, especially when the ground or bedding is hot. A percentage of your cows will be standing when the THI is over 70. Sand is much cooler than manure bedding. When a cow’s core body temperature reaches 39 C (102.2 F), she will get up and go to a soaker, if available, until her temperature reaches 38 C (100.4 F).

• It takes two days after the onset of heat stress to observe the maximum effects on production, due to reduced feed intake.

• Heat stress can reduce the birth weight of calves by 10 lb. due to the direct effect of heat on the dam and the growing fetus and indirect effect of a shortened gestation.

• You can use an infrared gun to help determine whether a cow is hot. Point it high on the flank. Skin temperatures over 35C (95 F) indicate heat stress.

• Cooling dry cows will result in at least 1,000 pounds more milk in the next lactation. Minimum protection for dry cows includes shade.

• Make sure hospital barns have excellent heat abatement. The reasons are obvious.

• When the air temperature is close to the cow’s body temperature, evaporative cooling is the only effective method of cooling. Blowing air that is hotter than the cow’s core body temp (101 F) on a cow only makes her hotter.

• Measure the summer-winter difference in average milk production of your herd to get a gauge on your heat abatement. In Arizona herds, it’s currently about a 9 lb. difference. In Israel, the difference is down to less than 2 lb., indicating what can be done to alleviate heat stress.

• Cows with the "slick hair gene" (from the Senepol breed) are more heat tolerant. Although cows don’t sweat well, slick hair cows have more sweat glands. With less hair, air flow over the skin results in more effective cooling.

• Cows follow shade by instinct. Because of this, stationary cooling systems under east-west facing shades are less effective as the shade moves. Cooling systems that follow the shade help.

For those who closely observe cow behavior, many of her responses to heat stress are obvious. Why do cows eat less when they’re hot? Try eating a bowl of Cheerios when you’re breathing 120 times/minute, says Dr. Collier.

Researchers have updated our understanding of the role that essential fatty acids, particularly omega-3 and omega-6 fatty acids, play in animal health, growth, production and reproduction.

A few years ago, I reported on a new topic that I called "omega breeding" (Omega 3 Breeding, Dairy Today, Fall 2007). Since then, researchers have been adding to our understanding of how essential fatty acids (EFA), particularly omega-3 and omega-6 fatty acids, play a role in animal health, growth, production and reproduction. A recent review of this topic was presented at the 2013 Florida Nutrition Conference.

Here are some things they have learned:

1. Interestingly, calves born from cows fed supplemental fat (both saturated and unsaturated) during the dry period may receive better passive immunity from their dam. IgG absorption was increased when dams were fed about 2% of their prepartum diet from supplemental fat. The calves out of these dams also produced more milk in their first lactation.

2. Calves fed milk replacers fortified with EFA (linoleic acid or omega-6) gained about 6.5 lb. more than controls by 60 days of age.

3. Fresh cows supplemented with 1.5% bypass fat (about 0.7 lb./day) averaged about 9.5 lb. more milk than non supplemented cows during the first three months after calving. When the fat contained EFA, the milk increase was even higher.

4. Recently, University of Florida researchers studied fertility in 1,380 cows fed EFA. Reproduction was significantly improved when cows were supplemented with EFA from safflower oil prepartum and then switched to EFA from fish oil at 30 days after calving. The response was due to fewer early embryonic pregnancy losses. This effect of feeding EFA has been very consistent.

Essential fatty acids (omega-6 and omega-3) need to be protected from rumen degradation for maximum effectiveness. These experiments used Calcium salts of the fatty acids for rumen protection. Even so, some of the fatty acids were still changed by biohydrogenation in the rumen, as evidenced by conjugated linoleic acids (CLA) found in the colostrum. Fresh grass is a good source of EFA. However, the bugs in the rumen hydrogenate or saturate most of it. That’s why they produce butter, instead of... cow oil.

Reference: The Role of Specific Fatty Acids on Dairy Cattle Performance and Fertility. 2013 Florida Ruminant Nutrition Symposium.

Stress, the release of cortisol and negative energy balance are other suspected culprits for problems during this critical lactation time.

Cows are more susceptible to infectious diseases and metabolic disorders around the time of calving because the immune system is at its weakest during this time. Mastitis, metritis and other infections respond to treatment much less at calving than at any other point in the cow’s lactation.

We don’t know the whole story about why cows have poorly functioning immune systems around the time of calving, but there are several theories, according to Matt Waldron at the University of Missouri. We know that stress and the release of cortisol at calving suppress the immune system.

Negative energy balance caused by the high demands for milk production and lower prepartum dry matter intake seems like an obvious culprit. Mastectomized cows have been shown to have better immune function than cows with intact mammary glands immediately following calving, indicating that the metabolic demands of the mammary gland stress the immune system. But experimentally induced feed restrictions during lactation have not resulted in the same immunosuppression as at parturition, so negative energy balance by itself doesn’t seem to be the cause.

Over-conditioned cows have a greater risk for inflammation and infection after calving, and the cause-and-effect puzzle is slowly being assembled, according to Waldron. Fat cows are more likely to have higher levels of circulating nonesterified fatty acids (NEFA) and ketones and also accumulate more fat in the liver. Elevated NEFA, ketones and liver triglycerides have all been associated with impaired immune function. Fat cows also tend to have higher levels of unstable oxidizing molecules that react with tissue fat, protein and DNA and contribute to inflammation.

Calcium is involved with proper immune system function. Cows with subclinical or clinical milk fever are more susceptible to mastitis.

So, how do we help immune function during this critical time in a cow’s lactation? Minimizing stress by providing a clean, comfortable environment for transition cows is number one. Avoid calving over-conditioned cows. The high price of cull cows lately should help this situation. Prepartum diets designed to minimize subclinical milk fever may also reduce the risk of mastitis and metritis. Providing adequate bioavailable antioxidant nutrients such as vitamin E, A, and zinc and selenium can help reduce inflammation and duration of infections, according to Waldron.

How do the top herds in reproductive performance get to be the 1%ers?

How do the top 1% of herds in reproductive performance get to be the 1%ers? What do they do that sets them apart? A survey conducted by researchers at the University of Pennsylvania compiled data from 16 herds that were nominated by their consultants based on excellence in reproductive performance. These producers ranged from 262 to over 6,000 lactating and dry cows.

Cow fertility has a biological component (the cow) and a management component. Fertility has decreased with increasing milk production over the years. Days open has increased from 110 days in 1965 to 150 days in 2005. There’s no question that fertility is influenced by high production. So, reproductive management has become ever more important and according to this survey, it’s what sets the 1%ers apart.

Pregnancy rate (PR) averaged 32% in the 1%ers compared to about 16% for all herds in the Raleigh Dairy Records Management System (DRMS). This put these herds in the top 1% for PR. These herds averaged 71 days to first service compared to 92 days for all herds in DRMS. Surprisingly, the 1%ers had only average conception rates compared to all herds in DRMS (44 % first service conception rate and 39% across all services vs. 43% for all DRMS herds).

Excellent heat detection and insemination rates resulted in the superior reproductive performance in the 1%ers. High insemination rates in these herds were due to controlled first insemination programs as well as consistent repeat insemination programs. They employed weekly or biweekly pregnancy checks combined with a resynchronization program. The 1%ers used a combination of timed AI and heat detection by visual and heat detection aids (paint, markers and activity monitors). In a nutshell, the 1%ers were aggressive and applied their reproductive programs consistently.

The herds in this survey were in the Midwest, Northeast and on the West Coast. There were no herds from the Southern states, where heat and humidity challenge reproductive performance. But the same intense reproductive management still applies if herds in the South want to improve reproductive performance.

Since this is primarily a nutrition column, I should mention that nutrition was not considered as a variable in this survey. I would assume that nutrition programs were also well managed in these 1%ers. No magic pill or nutritional supplement can substitute for hard work and superior management of a reproductive program.

Reference: Ferguson, J.D. and A. Skidmore. 2013. Reproductive performance in a select sample of dairy herds. J.Dairy Sci. 96:1269-1289.

Rick Lundquist is an independent nutrition and management consultant based in Duluth, Minn. Contact him at siestadog@aol.com.
 

I recently enlisted the help of Novus International on several of my clients’ dairies to study our cow comfort. They installed data loggers on the cows to monitor feeding behavior, lying time and standing and walking time.

The results revealed that our management procedures were often designed for our convenience and not for our cows.

The overall management of a cow’s environment and time budget has a huge impact on feeding, resting and rumination, which in turn impacts cow health and production. Cows should have the opportunity to lie down 10 – 12 hours/day. Anything less will increase the risk of lameness and will reduce potential milk production and fertility.

We found that our stall design and time away from the stalls were our biggest bottlenecks. Cows won’t want to lie down if they have uncomfortable stalls. They can’t lie down if they are kept away from their stalls or locked up too long. Maybe the distance to the parlor is too far or the pen size is too large or we’re just getting them up too soon.

Two things jumped out at us when the data were analyzed. First, many of the cows were away from their pens too long. Our cow pushers were getting them up before the cows needed to. This was for their convenience, not for the cows.

They were standing on concrete, away from their stalls much longer than the goal of about 3 hours/day. This was an easy fix.

Second, our neck rails were too low and too close to the curb. The target for neck rails, according to University of Wisconsin researchers, is 48" or higher above the bedding and 68" or more from the curb.

Why do we have neck rails? To keep the stalls clean. No consideration for cow comfort. We observed cows contorting around the neck rails to lie down or get up in their stalls. Some were perching with their hind feet in the alley.

My clients decided to raise their neck rails and move them forward. One considered removing them all together. In the end, the cows didn’t need them, so why did we have them? For our convenience, so we didn’t have to scrape manure from the back of the stalls. We decided that regular removal of manure from the stalls also got someone in the pens more often to observe the cows.

These dairies were in Florida, so good clean sand is readily available. They all did a good job of keeping beds full.

Lying time decreases about 30 minutes for each inch decline in bedding level in deep bedded stalls, according to researchers at the University of British Columbia

Stocking rate was one item that really didn’t correlate with performance in these herds. We ranged from 82% stocking rate (cows/stall) to 132%. The herds with the higher stocking rates had better cow comfort scores and better overall performance.

This indicated to me that when we tend to our cows’ overall comfort, we not only get better health and production/cow, but we can milk more cows in the same facility.

TABLEHEAD: 24-Hour Time Budget of a Dairy Cow

• Eating:  5 hours/day
• Lying (resting):  12-14 hours/day
• Standing, walking, idling:  2-3 hours/day
• Drinking: 0.5 hours/day
• Milking:  2.5-3.5 hours/day

Source: Rick Grant, William H. Miner Agricultural Research Institute

Rick Lundquist is an independent nutrition and management consultant based in Duluth, Minn. Contact him at siestadog@aol.com