While decreased production and weight gain often are immediate side effects of summer heat, decreased reproductive performance is another outcome that can cause long-term economic losses for dairy producers. In addition to adopting management techniques that help reduce heat stress, producers can improve reproductive efficiency by implementing strategic estrus-synchronization programs, using artificial insemination (A.I.) and breeding cows with highly fertile semen.

"At this time of year, providing cows with convenient access to shade and ample supplies of cold water, and avoiding overcrowding are important keys to managing heat stress," says Mel DeJarnette, reproductive specialist, Select Sires. "Despite the best heat-management techniques, however, keeping fertility high during the summer is still a challenge. Even though it can be tempting to use a herd bull, top producers continue to use A.I. year-round, recognizing that heat stress affects the fertility of bulls too."

Bull Fertility Suffers in Summer Heat, Too

Researchers at Virginia Tech, Blacksburg, Va., have conducted research to better understand the effects of heat stress on semen production in bulls. One study involved collecting semen at three-day intervals for a 10-week period. After establishing baseline semen production, the researchers mimicked heat stress by covering the scrotum of each bull with a sock made of insulated batting material for 48 hours.

They found that semen quality began to decline approximately nine days after the thermal insult, and that the maximum effect was not observed until 18 days after the insult. Semen quality then began to rebound, but normal levels were not regained until 35 to 40 days after the sock had been removed. Since the production of a sperm cell takes approximately 63 days from start to finish, even a short-term heat stress can affect the semen quality of herd bulls for as much as 1½ months.

"Extended periods of heat stress also can negatively affect semen quantity and quality, and can decrease the bull’s libido," says DeJarnette. "The bottom line is that you can’t depend on a herd bull to get cows bred during the summer. That’s why more producers turn to highly fertile frozen semen that has met stringent quality-control standards, including semen from sires that have been designated as SUPERIOR SETTLERs™."

Getting Cows Bred in Hot Temperatures

Research has shown that cows experiencing heat stress in the southeastern United States have shorter and less-intense heats than cows in more temperate environments. Heat-stressed cows are reluctant to spend energy mounting and in other physical activity that would increase their body temperature. So while cows typically continue to cycle normally (every 18 to 24 days), it is harder to catch them in heat.

Heat-stressed cows, however, do respond extremely well to prostaglandin injections. That’s why estrus-synchronization programs can be implemented effectively in conjunction with environment-management programs.

"Synchronizing groups of cows during hot weather can make heat detection easier and more efficient," says DeJarnette. "This, along with intensive management of heat detection and breeding, should help maximize pregnancy rates."

What Can Producers Do?

Throughout North America dairy herds experience stress due to summer heat, resulting in decreased production and reproduction performance. Although producers cannot change the weather, they can adopt simple, inexpensive management changes to help restore performance during the summer season.

Time-tested mechanical aids, such as fans and misters, continue to be cost-effective options in the battle against heat. Since cows often reduce their feed intake by as much as 25 percent during heat stress, increasing the protein and energy content of feed while reducing fiber intake can help.

When it comes to managing reproduction, using estrus synchronization and A.I. are always important tools.

"The best way to get more bang from your heat-detection buck is to use some form of estrous synchronization," says DeJarnette. "In addition, fixed-time A.I. options (e.g., Ovsynch) allow pregnancies to be achieved in the absence of heat detection, enabling many producers to cruise through the summer months with only modest declines in reproductive performance.

"It’s not too late to work with your veterinarian and other reproductive specialists to develop a program that can help right now," he continues. "In preparation for the summer, producers can reduce the number of cows needing to be bred during the hottest months by strategically using a synchronization program next spring."

August 2007

While the greatest variables affecting pregnancy rates are the accuracy of heat detection, inseminator technique and other management factors, looking at fertility values of individual sires can help. For years Select Sires has placed the SUPERIOR SETTLER™ designation on sires that meet stringent requirements for semen fertility. Trust Select Sires as your source of highly fertile semen and balanced genetics - because you want more than just a pregnancy.

"Select" sires designated as SUPERIOR SETTLERS based on a combination of their current semen quality and historic non-return data.

SUPERIOR SETTLER        MILK    %REL    TYPE   %REL

7HO5710	DANE		+889	99	+1.18	99
7HO6512	CLASSIC		+689	91	+.87	83
7HO6682	MARMAX		+2,104	99	+1.28	97
7HO6695	LC		+1,031	91	+1.12	85
7HO6745	ONYX		-344	96	+1.52	92
7HO6838	MATCHES		+1,719	88	+1.67	84
7HO7037	MILES		+23	88	+2.30	86
7HO7193	DESIGN		+2,189	97	+2.16	94
7HO7218	LYLE		+1,192	91	+2.01	87
7HO7285	HHF		+529	91	+2.19	87
7HO7452	FRITZ		+1,568	90	+2.06	86
7HO7455	GRANGER		+941	88	+2.23	85
7HO7463	PONTIAC		+873	90	+2.41	86
7HO7466	MOSCOW		+1,589	97	+2.19	94
7HO7536	COLDSPRING	+682	89	+2.23	87
7HO7544	FRASIER		+1,197	87	+2.03	86
7HO7560	BLITZ JINTX	+2,525	96	+1.62	91
7HO7650	JACKSON		+850	97	+2.64	92
7HO7785	REAGAN		+1,128	90	+2.39	87
7JE590	ACTION		+475	92	+2.3	82
7JE620	MAXIMUS		-18	96	+1.0	93
7JE681	TELMARK		+449	86	+0.6	75
7JE714	MATINEE		+719	78	-0.1	79

* = New Active Sire

Based on advanced laboratory semen quality evaluation techniques, these sires have the best probabilities of becoming SUPERIOR SETTLERS in the future.

SUPERIOR SETTLER        MILK    %REL    TYPE   %REL

7HO7514	RE DESIGN	+478	86	+2.65	72
7HO7653	ROSS *		-137	83	+3.27	68
7HO7712	SOCRATES	+1,462	88	+2.21	86
7HO7725	ALLOCATE *	+1,457	88	+0.62	86
7HO7737	MENDEV *	+1,438	85	+1.97	83
7HO7762	FLINT		+1,390	87	+2.19	86
7HO7838	GLEN		+882	88	+2.77	85
7HO7895	SEGER		+1,594	87	+1.67	86

7JE679	RAY		+468	85	+1.5	74
7JE712	AWARD		+29	92	+1.3	88
7JE731	LOTT		+1,374	85	+0.8	75

* = New Active Sire

™SUPERIOR SETTLER is a trademark of Select Sires Inc.