Spaying is a management tool long used by ranchers and cattle feeders. It's proven to have many advantages that outweigh just a few disadvantages.

Spaying females to surgically remove ovaries eliminates the primary source of estrogen, the estrus-causing hormone. It also removes the source of ova, which combine with sperm cells after mating to initiate pregnancy and the production of the progesterone hormone.

Spaying techniques

Once very common but now rarely used in the U.S., flank spaying involves an incision being made in the heifer's left flank, through which the ovaries are removed. This procedure is much more labor intensive and costly than modern vaginal methods now used.

Flank spaying also incurs occasional incision site infections. And, scarring at the incision site is common, which interferes with the hide pulling process at harvest resulting in excess carcass trimming.

In contrast, vaginal spaying is accomplished through the vagina. Vaginal spaying is much faster and less stressful on heifers. It also reduces the risk of infection or other complications associated with flank spaying. In addition, many more animals can be safely spayed in a day's time using the vaginal technique, which lowers overall labor costs. As with any surgery, the experience and proficiency of the surgeon is critical.

Two types of instruments are commercially available for vaginal spaying:

• The Kimberling-Rupp instrument is a tube-within-a-tube mechanism. It allows the ovaries to be excised and removed from the heifer vaginally.

• The Ovarian-Drop method involves a small-diameter, stainless-steel rod with an arrowhead-shaped end open in the middle. When the ovaries are excised, they're allowed to drop into the abdominal cavity for absorption by the body. Harvest examination of numerous groups of heifers has revealed no re-attachment of excised ovaries within the abdominal cavity.

Performance after spaying

It's been reported previously that spayed heifers had a performance disadvantage compared to intact heifers. Those studies, however, all involved heifers spayed with the flank method and no use of growth promotant implants.

This isn't the case when comparing implanted spayed and implanted intact heifers. For spayed heifers, the source of progesterone and most of the estrogen source has been removed. Therefore, it's important to implant spayed heifers.

Studies show spayed heifers respond more positively to implants than intact heifers. Spayed heifers can be grazed, fed and implanted in a manner similar to steers.

One study showed the average daily gain response to implantation was four-fold greater in spayed than in intact heifers. Heifers spayed and implanted tended to deposit more lean tissue and less fat during this experiment (Table 1).

Other grazing/growing studies have shown an overall 5.5% gain advantage (0.12 lbs./day) for spayed implanted heifers vs. implanted intact heifers (Table 2).

Finishing studies have shown a 2.5-3% gain advantage for spayed implanted heifers. Feedlot surveys indicate a 0.1-0.3 lbs./day advantage for spayed implanted heifers (Table 3).

Losses due to pregnancy

A pregnant heifer calving in the feedlot costs the feeder $150-$200 due to calving problems, infection, and decreased gain, carcass quality and yield.

A 1984 survey of feedlots and packers found almost 15.5% of feeder heifers were pregnant at feedlot arrival. The total cost to pregnancy-test and abort, or inject all heifers to abort those pregnant, averaged 5.29% of the purchase price of the heifer. This includes added charges for observation, managing dystocias, retained placentas and treatment.

Meat packers estimate the average loss in carcass yield for pregnant heifers is 3.3%. Data on more than 10,000 heifers shows an average carcass yield decrease of 5.6% on pregnant heifers. Based on carcass weight gain, pregnant heifers gained 12.6% less and had a 13.3% higher feed conversion rate than non-pregnant heifers.

Research trials indicate spayed heifers in the feedlot — implanted and marketed at the correct time — have a 2% gain advantage compared to implanted intact heifers. The advantage is based on a combined average of studies over a six- to seven-year period on spayed yearling heifers shipped to feedlots.

The spayed heifer will reach optimum grade sooner than her intact counterpart. Good quality spayed heifers finish and grade at 90-110 days on feed, and yield a quality carcass.

It's clear that spayed heifers implanted and marketed at the proper time will outperform their intact counterparts. Feedlot operators realize these figures, coupled with potential problems of abortion, calving/dystocia problems and increased labor costs of pregnant heifers, make pregnant heifers a definite feedlot liability.

Spaying also eliminates the visual exposure of heifers calving in a feedlot setting, which can harm public perception of both the individual feedlot and the overall industry regarding animal welfare and care.

Daryl Meyer, DVM, is a practicing veterinarian in Fremont, NE. Reach him at darylmeyer@qwest.net or 1-800-494-1045.

Table 1. Effect of spaying and anabolic implants on growth of beef heifers.

	Intact			Spayed
		No implant	Synovex H	No implant	Synovex H	Synovex S
Initial wt. (lbs.)		607	600	605	596	585
Final wt. (lbs.)		946	970	902	990	1,001
Daily gain, lbs.
	Growing	2.20	2.51	1.96	2.77	2.64
	Finishing	2.53	2.66	2.20	2.66	3.10
	Overall	2.40	2.60	2.09	2.75	2.93
Feed/gain
	Growing	7.28	6.49	7.67	5.75	5.71
	Finishing	6.36	6.24	6.59	6.10	5.62
	Overall	6.70	6.35	7.04	5.97	5.65
Adj. hot
	carcass wt. (lbs.)	592	616	559	620	640
Results from this study indicate it's necessary to implant spayed heifers to maximize growth performance. Spayed, implanted heifers tended to gain more rapidly and efficiently than intact, implanted heifers. Because gonadectomy of the heifer renders her nearly the endocrine equivalent of a steer by eliminating ovarian estradiol and progesterone, the estradiol-progesterone implant may be the more appropriate combination for the spayed heifer.

Table 2. Gain data summary of six trials comparing implanted spayed heifers and implanted non-spayed heifers grazing or on growing rations.

No. spayed/No. intact	Feed/ration	Spayed ADG (lbs.)	Intact ADG (lbs.)	% diff. ADG	Year
32/33	Grazing	1.98	1.89	4.55	19811
35/35	Grazing	1.98	1.85	6.57	1981
54/27	Grazing	1.71	1.62	5.26	19832
54/27	Grazing	1.74	1.62	6.90	1983
398/73	Growing	1.47	1.48	-0.67	19863
18/17	Growing	2.77	2.5	10.36	19904
Average		1.90	1.83	5.50%
See footnotes below

Table 3. Gain data summary of seven trials comparing implanted spayed heifers and implanted non-spayed heifers on finishing rations.

No. spayed/No. intact	Feed/ration	Spayed ADG (lbs.)	Intact ADG (lbs.)	% diff. ADG	Year
101/117	Finishing	4.14	3.82	7.73	19875
31/44	Finishing	4.01	3.96	1.25	1987
35/38	Finishing	4.25	4.01	5.65	1987
39/38	Finishing	4.06	3.91	3.69	1987
32/33	Finishing	2.39	2.26	5.44	19816
35/35	Finishing	2.25	2.39	-5.86	1981
17/18	Finishing	2.66	2.66	0.00	19907
Avg.		3.39	3.29	2.56%

¹ Rush IG, Reece PE: Spaying and Implanting growing and finishing heifers. Nebraska Coop Ext Serv Beef Cattle Rep EC81-218:35-38, 1981

² Shoop MC, Rupp GP, Kimberling CV, Bennett BW: K-R spaying, anabolic agent (Zeranol), and pasturing spayed heifers with steers: Their effect on growth of stocker cattle. Proc West Sect Am Soc Anim Sci: 35, 1984

³ Cain DV, Jones AL, Milliken G: Do different spay techniques and growth implant frequencies affect weight gain in heifers? Vet Med 81(5): 464-468, 1986

⁴ Same as 4.

⁵ Rupp, GP: Why Spay Heifers? Bovine Prac 19:156-160, 1987

⁶ Same as 5.

⁷ Same as 4.

The pros and cons of spayed heifers

Advantages

• Maintains stocker and feeder heifers in an “open” or neutered status.

• Makes for early detection of pregnant stocker heifers accidentally bred at a young age.

• Prevents pregnant heifers in a feedlot situation with all the associated complications of C-section surgeries, vaginal/uterine prolapses, down and dying heifers and frustrated feedlot personnel.

• Eliminates need for feeding estrous-suppression feed additives, saving $2-$4/head during the feedlot phase.

• Eliminates pregnancy checking (palpating) of heifers on feedlot arrival, saving $1.50-$2/head, plus labor costs.

• Eliminates need to test stocker heifers from specific areas for brucellosis and/or tuberculosis when marketed to out-of-state feedlots, saving $1.50-$3/head, plus labor costs.

• Improved daily gain and feed conversion when spayed heifers are implanted vs. intact implanted heifers.

• Ability to graze/feed heifers and steers together.

• Ability to graze spayed heifers near cow-calf herds with bulls present.

Disadvantages

• Surgery is irreversible. Spayed heifers are no longer candidates for breeding as replacement heifers.

• Typical cost is $5-$6/head depending on the number being spayed at one location.

• Minimal risk of death loss related to the surgery, depending on the surgeon's expertise.