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Safety & Health

Appendix B: Overall Reproductive Efficiency and Health Statistics for US Animal Agriculture

In order to gain a better understanding of the animal safety issues associated with SCNT, it is helpful to review statistics on animal health and reproduction under current agricultural practices. This section draws data from reports published by USDA/APHIS National Animal Health Monitoring System (NAHMS at http://www.aphis.usda.gov/vs/ceah/ncahs/nahms/index.htm) and the National Agricultural Statistics Service (NASS at http://www.nass.usda.gov/census/census02/volume1/us/index1.htm).

A. Dairy cattle

The Dairy 2007 Part I: Reference of Dairy Health and Management Practices in the United States report (USDA/NAHMS 2007) surveyed a total of 2,194 dairy operations in the United States. According to the USDA/NASS census, in 2002, there were 9,109,600 milking dairy cows in the United States. The predominant breed of dairy cattle in the US is Holstein, comprising 93.4 percent of the national herd. The next most popular breed is the Jersey, comprising about 3.6 percent of dairy cattle in the US. Other “colored” breeds (Guernsey, Brown Swiss, Ayrshire, and others) make up the remaining minority, and numbers for these breeds are more variable. Individual dairies vary in size from fewer than 100 to as many as 10,000 cows. Due to the variability in size of dairies, the USDA/NAHMS report broke dairies down into three groups: fewer than 100 cows, 100-499 cows, and greater than 500 cows. The report does not supply statistics for individual breeds of dairy cattle.

According to the USDA/NAHMS 2007 report, the most commonly reported causes of cow illness for all operations were clinical mastitis, lameness and infertility problems (failure to conceive by 150 days postpartum). Incidence of retained placenta was also a commonly reported problem (7.8 ± 0.2 percent), and may have contributed to incidence of reproductive problems. Incidence of clinical mastitis was similar across operations, and averaged 16.5 percent of all cows. Table B-1 presents data on causes and incidence rate of illness for operations responding to the survey.
Table B-1: Most commonly reported health problems contributing to morbidity, mortality and culling of US dairy cattle

Cause % morbidity 1 % mortality 2 % culled 3
Clinical mastitis/udder problems 16.5 ± 0.5 16.5 ± 0.7 23.0 ± 0.6
Lameness 14.0 ± 0.4 20.0 ± 0.8 16.0 ± 0.4



Retained fetal membranes

Other (dystocia, metritis)


12.9 ± 0.3

7.8 ± 0.2

4.6 ± 0.3




15.2 ± 0.7 4

26.3 ± 0.7 5


1 Expressed as percentage of all cows ± standard deviation of the mean.

2 Expressed as percentage of cows dying ± standard deviation of the mean.

3 Expressed as percentage of cows culled ± standard deviation of the mean.

4 Mortality attributed to dystocia

5 Culling for all reproductive problems

The percent of dairy cows dying in 2002 was 5.7 ± 0.1 percent, and did not differ by size of operation. The most frequently reported causes of death for all dairy cows in this report were lameness or injury (20.0 ± 0.8 percent), mastitis (16.5 ± 0.7 percent), and difficult labor, also known as dystocia (15.2 ± 0.7 percent).

Mastitis may cause death by acute toxicity, or cows may be euthanized as a result of severe or persistent mastitis caused by treatment-resistant pathogens such as Staphyloccocus aureus or Mycoplasma species. The percent of cows culled for mastitis or other udder problems in 2007 was 23.0 ± 0.6 percent for all cows culled, and represented one of the most common reasons for culling. Culling due to reproductive problems was an equally common reason given by producers in this report (26.3 ± 0.7 percent of all cows culled), with poor production not due to illness as the next most common reason (16.1 ± 0.7 percent of all cows culled). On average, 23.6 ± 0.3 percent of dairy cows were culled in 2002, with culling rate slightly higher on smaller dairies (24.1 ± 0.6 percent for herds with fewer than 100 cows) compared to medium dairies (23.7 ± 0.5 percent for dairies with 100 to 499 cows) and 23.4 ± 0.7 percent for large operations (more than 500 cows).

Mortality for dairy cattle varied by age, with unweaned heifers having the highest death rate (8.7 ± 0.2) and weaned heifers having the lowest death rate (1.9 ± 0.1 percent). Smaller operations appeared to have a higher death loss among unweaned heifers compared to operations with more than 500 milking cows (9.1 ± 0.4 and 9.4 ± 0.3 percent for operations with less than 100 cows and between 100 and 500 cows, vs. 7.7 ± 0.5 percent for operations with greater than 500 cows).

Table B-2 presents data on causes of death and incidence rate for weaned and unweaned heifers for all operations responding to the survey.

Table B-2: Major causes of mortality for unweaned and weaned dairy replacement heifers that died

Cause Unweaned Weaned
Diarrhea 56.5 ± 1.3 1 12.6 ± 1.0
Respiratory 22.5 ± 0.9 46.5 ± 1.7
Dystocia 5.3 ± 0.7 NA

1 Percentage of deaths ± standard deviation of the mean.

In the US, most dairy cattle are bred by AI, although many dairies still maintain bulls for cows that do not conceive to AI. According to the USDA/NAHMS 2007 report, 51.7 percent of dairies surveyed maintained one or more bulls. Embryo transfer has been promoted as a commercially feasible assisted reproductive technology (ART) for dairy cattle, particularly for dairies interested in using their best cows to improve herd genetics (Webb and Drost 1992). Embryos are also sold nationally and internationally to increase genetic advancement and overall herd production. The International Embryo Transfer Society, a professional society whose membership includes breeders and researchers, estimates that a total of approximately 670,711 in vivo derived bovine embryos were transferred worldwide in 2006 (Thibier 2007). Cows with less desirable genetics or production levels may be used as recipients of higher genetic merit embryos. However, ET is not a predominant means of reproduction in dairy cattle. In vitro fertilization has been less successful than in vivo fertilized ET, and is not commonly practiced. The developmental competence of cultured bovine embryos remains low (Betts and King 2001), with less than half of bovine IVF embryos developing to blastocysts, and even fewer survive to attachment in the uterus.

In cows bred by AI, pregnancy may be diagnosed by ultrasound 35 days after insemination or by palpation approximately 40 to 45 days after insemination. Average pregnancy loss following a positive pregnancy diagnosis for all cows across operations of different sizes was 4.5 ± 0.2 percent. Pregnancy loss was highest on larger operations (5.3 ± 0.3 percent for operations with greater than 500 head; 3.7 ± 0.1 percent for operations with less than 100 head; 3.7 ± 0.3 percent for operations with 100 to 499 head) (USDA/NAHMS 2007).

B. Beef Cattle

Beef cattle in the US are managed under various systems, depending on the intended use of the animals. Beef cattle destined for slaughter may change hands several times before final disposition. Breeding stock and young nursing animals may be maintained on range or in pasture. These are generally referred to as “cow-calf” operations. Following weaning, animals destined for slaughter may go directly to feedlots or may be maintained for a brief period on high quality pasture, a stage referred to as “back-grounding” or “stocker.” In the US, most cattle are slaughtered between 15 to 18 months of age.

The 1997 Beef Cow-Calf Health and Health Management Practices report (USDA/
NAHMS) surveyed 2,713 beef cow-calf operations throughout the United States, representing an estimated 34,280,000 head of cattle. According to the survey, approximately 1.5 ± 0.1 percent of breeding cattle, including weaned replacement heifers, cows and bulls, died or were euthanized due to various causes in the previous year. Mortality rate was higher on small operations with less than 50 cattle, compared with larger herds (2.4 ± 0.3 percent). Approximately 20 percent of these losses were due to unknown causes. The largest single category (27 percent) of losses for beef breeding cattle was “other known” causes, most of which producers attributed to old age. The next highest categories (after “unknown”) were weather (18.0 percent) and calving problems (17.0 percent). Table B-3 presents the leading known causes of death, where a specific cause was named, for cattle that died.

Table B-3: Causes of death for beef breeding cattle (cows, bulls and weaned replacement heifers) that died

Cause Percent ± SE
Digestive 6.1 ± 0.1
Respiratory 6.0 ± 1.0
Weather 18.0 ±3.9
Dystocia 17.0 ± 1.9

Relatively few breeding females in cow-calf herds experienced health problems, according to the 1997 survey. In general, replacement heifers experienced a higher percentage of illnesses compared to mature cows. Pinkeye was the most commonly reported illness, and occurred in 1.3 percent of female breeding cattle. With the exception of pinkeye, illness rates for breeding females appeared fairly similar among herds of different sizes. Pinkeye incidence was reported highest in small herds (less than 50 head, 2.3 percent) than in large herds (more than 300 head 0.6 percent). There was no difference in incidence rate of retained placenta or uterine infections between small and larger operations (0.2 ± 0.0 percent for operations with less than 50 or more than 300 head). Incidence of pregnancy loss was also small and not significantly different between breeding females in different sized herds (0.2 ± 0.1 percent in herds with less than 50 head; 0.3 ± 0.0 percent in herds with greater than 300 head). Major causes of health problems in breeding female beef cattle are listed in Table B-4.

Table B-4: Causes of morbidity in breeding female beef cattle 1

Conditions Replacement Heifers Cows All Females
Respiratory Disease 0.9 ± 0.3 2 0.3 ± 0.0 0.4 ± 0.1
Scours 1.0 ± 0.2 0.4 ± 0.1 0.5 ± 0.1
Pinkeye 1.9 ± 0.4 1.2 ± 0.1 1.3 ± 0.1
Cancer eye 0.0 ± 0.0 0.3 ± 0.0 0.2 ± 0.0
Foot rot 0.8 ± 0.2 0.8 ± 0.1 0.8 ± 0.1
Mastitis N/A 0.2 ± 0.0 0.2 ± 0.0
Retained placenta/metritis N/A 0.4 ± 0.0 0.3 ± 0.0
Spontaneous abortion 0.3 ± 0.1 0.3 ± 0.0 0.3 ± 0.0
Neurologic problems 0.0 ± 0.0 0.1 ± 0.0 0.1 ± 0.0

1 Expressed as average percentage of all breeding females in 1996 cattle inventory.

2Percentage of females by category ± SE.

Average mortality rate of unweaned calves was approximately 3.4 ± 0.1 percent of all calves born during 1996, and there were no appreciable differences among operations of different sizes for calf mortality. Two of the most common causes of death, when death could be attributed to a cause, were respiratory problems and dystocia. The leading causes of calf mortality according to producers surveyed are expressed in Table B-5.

Table B-5: Most common perceived causes of death for unweaned calves

Cause Percent ± SE

14.4 ± 1.0


16.3 ± 1.2


20.2 ± 1.4


13.9 ± 1.3


17.5 ± 1.4

The leading cause of morbidity in calves was scours (diarrhea) affecting 2.4 ± 0.2 percent of all calves three weeks old or younger. Older, but still unweaned calves had a slightly lower incidence of scours (1.7 ± 0.2 percent). Diarrhea, in part, may have contributed to death losses due to digestive problems. Causes of morbidity in unweaned calves are listed in Table B-6.

Table B-6: Causes of morbidity in unweaned calves 1

Cause 3 Weeks or Less Over 3 Weeks Old
Respiratory 0.5 ± 0.1 2 0.8 ± 0.1
Scours 2.4 ± 0.2 1.7 ± 0.2
Pinkeye 0.1 ± 0.0 1.1 ± 0.1
Foot rot N/A 0.2 ± 0.0

1 Based on all calves in survey.

2 Mean Percentage ± standard error.

C. Swine

The total US swine population was estimated at 59,848,000 head in 2000 (USDA/NAHMS 2001). Most US swine operations are fully integrated. This means that swine remain on the same operation under the same general management throughout their lives. Animals are usually maintained under full confinement in highly biosecure facilities, to minimize disease transmission and for other economic and management reasons. Sows generally farrow (give birth) twice a year. Piglets remain with their dams for approximately 21 days, and then are weaned and moved to a nursery, where they are housed in small groups in raised pens for 6 to 8 weeks. They progress through “grower” and “finisher” phases, depending on weight, and are generally maintained in the same groups throughout the process.

The most complete survey of swine health and management practices in the United States was published in 2001. This section derived data from Part I: Reference of Swine Health and Management in the United States, 2000 and Part II: Reference of Swine Health and Health Management in the United States, 2000 (USDA/NAHMS 2001). A total of 2499 producers were surveyed for the report. In order to qualify for the report, operations must have had at least 100 head of swine at the time of the survey.

A total of 3.3 ± 0.1 percent of all breeding females died and 17.5 ± 0.7 percent were culled between December 1999 and May 2000. The most common reasons cited for culling were age, lameness, performance and reproductive failure. Measures of poor performance in this survey included small litter size, high pre-weaning mortality and low birth rate. Other reasons for culling included upgrading herd genetics, poor body condition and liquidation of the breeding herd for financial reasons. Table B-7 presents the reasons for culling and the relative percentages of swine culled for those reasons.

Table B-7: Reasons for culling swine

Cause Percent of culled females ± SE Percent of all females ± SE
Age 41.9 ± 1.8 7.3 ± 0.4
Lameness 16.0 ± 1.2 2.8 ± 0.3
Performance 12.0 ± 0.7 2.1 ± 0.1
Reproductive failure 21.3 ± 1.3 3.7 ± 0.2
Other 8.8 ± 1.6 1.6 ± 0.3

The two most commonly reported health problems in breeding females were roundworms (an intestinal parasite) and Porcine Reproductive and Respiratory Syndrome (PRRS). Swine dysentery was the only health problem more commonly reported on small operations (less than 250 swine) compared to large operations. Other diseases occurred at a higher rate on larger operations. Unfortunately, no data were presented to indicate number or percent of animals affected by disease. Problems at farrowing and other reproductive problems were not reported.

D. Sheep

Most sheep in the US are raised for the production of both wool and meat. In the Eastern US, most sheep are raised on farms in fenced pasture, and may be supplemented with grain. In the Western US, it is more common to maintain sheep on open range. Lambs are generally born in late winter or early spring. Age at slaughter is variable, depending on the price of lamb compared to the price of grain and other inputs.

The National Agricultural Statistics Service (NASS), USDA reported 66,100 sheep operations with a total national herd of 6,965,000 head as of February 2002. The 2001 Reference of Sheep Management in the United States (USDA/NAHMS) reported that 23.8 ± 1.0 percent of rams and 18.3 ± 0.5 percent of ewes in all flocks were culled in 2000, and 5.0 ± 0.1 percent of all sheep and lambs died. Sheep raised on farms had a marginally higher death loss compared to open or fenced range sheep (5.6 vs. 4.5 and 4.7 percent, respectively). Data on culling rates by type of operation were not available. Table B-8 presents primary reasons for culling by sex for animals culled in 2000.

Table B-8: Primary reasons to cull for all rams and ewes culled

Reason for Culling Rams Ewes
Age 47.7 ± 2.1 1 47.9 ± 1.8 2
Teeth problems 0.8 ± 0.3 5.3 ± 0.5
Poor mothering N/A 3.3 ± 0.3
Mastitis N/A 3.3 ± 0.2
Failure to lamb N/A 5.5 ± 0.4
Ram breeding soundness 13.8 ± 1.4 N/A
Other reproductive 3.6 ± 1.1 1.2 ± 0.4

1 Percent of all culled rams ± SE

2 Percent of all culled ewes ± SE

Predators (23.5 ± 1.0 percent), dystocia (12.3 ± 0.5 percent) and old age (15.4 ± 0.8 percent) accounted for 51.2 percent of all adult sheep that died or were lost in 2000. Other problems included respiratory disease, other diseases, digestive and metabolic problems (including milk fever and pregnancy toxemia), poisoning/toxicity, weather, and theft. Table B-9 presents data on major causes of death for adult sheep and lambs that died in 2000.

Table B-9. Causes of death for adult sheep that died in 2000

Cause Sheep Lambs
Predators 23.5 ± 1.0 1 44.1 ± 1.1 2
Digestive 6.7 ± 0.6 9.9 ± 0.6
Respiratory 7.0 ± 0.8 11.7 ± 0.7
Metabolic 3.7 ± 0.4 1.0 ± 0.1
Dystocia 12.3 ± 0.5 NR 3
Other disease 3.0 ± 0.2 2.0 ± 0.3

1 Based on percent of all sheep that died ± SE

2 Based on percent of all lambs that died ± SE

3 Not reported

As for swine, incidence and causes of morbidity in sheep was presented as percentage of operations reporting the problem. Data on number or percent of animals affected by illness were not presented in the USDA/NAHMS report. The most commonly reported health problems were stomach or intestinal parasites, clostridial infection, contagious ecthyma (sore mouth), and foot rot. Respiratory and reproductive problems were not reported as causes of illness in sheep or lambs in this report.

E. Goats

Statistics on goat production in the US were not available through USDA/NAHMS. According to the Agriculture Databases for Decision Support (ADDS), there are approximately 2 to 4 million goats raised in the US (http://www.adds.org/CGI-BIN/om_isapi.dll?clientID=23885&infobase=National%20Goat%20Database&softpage=Browse_Frame_Pg). However, no reliable or comprehensive statistics on goat numbers or their production in the US could be found. Goats are generally divided into three distinct types for meat, dairy or fiber (mohair or cashmere) production. Goats grown for meat or fiber are raised predominantly in large herds on open range, while dairy goats are raised in smaller herds on limited acreage with grain feeding. Intestinal parasites and respiratory diseases appear to be the most common illnesses reported in goats, although actual data were not available (ADDS Goat Handbook 1993).