Take Home Messages

• Atresia coli does not have a simple etiology.
• BLAD tagged along in an outstanding family.
• Citrullinemia is not a marker for economically important traits.
• DUMPS is the forgotten genetic defect because the industry aggressively eliminated carriers.

Atresia coli

A healthy calf is born with a good appetite but then in a day or two the calf bloats, loses appetite and becomes lethargic. The calf has not defecated. Although the calf appears normal on the outside, the calf may have a constriction or blockage in the intestine. Surgery is possible but the prognosis is not good. Death usually occurs within a week because the unexpelled fecal material poisons the calf.

Why does atresia coli happen? Research is currently underway to distinguish between a genetic and environmental cause. Both causes have been purported in the literature. Our earlier research had indicated that genetics contributed to atresia coli. Research from Germany implemented early palpation for pregnancy as an environ- mental cause. Reviewing our data, most, but not all, dams of atresia coli calves had been palpated for pregnancy before day 40. No one cause fits all the data.

BLAD

Type production index (TPI), and predicted transmitting abilities (PTA) for dollars fat, dollars protein, milk, percent fat, fat, percent protein, protein, and type were the nine traits analyzed to determine associations with normal or carrier status of Bovine Leukocyte Adhesion Deficiency (BLAD).

The frequency of BLAD by summary date was calculated by direct counting (Table 1). Only carrier and normal bulls were used in the analysis to give a total of 884 bulls. Nontested new bulls increased from a low of 14 in January 1994 to 41 in January 1995. Overall, the number of carrier bulls has decreased.

Of the 91 sires that had 884 sons, 8 were BLAD carriers that had 117 sons. The frequency of BLAD was calculated within family for bulls of carrier sires (Table 2). Three of the four sires with more than five sons had more normal sons than carrier sons. This may suggest that a few borderline BLAD carriers were culled when their borderline normal brothers were kept.

Using a simple analysis (Table 3), normal bulls had an advantage in PTA type. Performances of bulls were not significant (P<.05) for the interaction of BLAD and first summary. These results may be interpreted that BLAD should be considered a marker for quanti- tative trait loci or that families with BLAD carriers have some characteristics unique from the rest of the population.

When evaluating the data for the same traits under a more complex model that considered relationships among the bulls (Table 3), no significant differences (P<.05) were found between BLAD carriers and normals. These results suggest that the families with BLAD carriers had type characteristics unique from the rest of the population.

From the time of first public testing in January 1992, the frequency of BLAD carriers among the top 400 AI active bulls has decreased. After adjusting for relationships, no associations were observed between predicted transmitting abilities and status for BLAD.

Citrullinemia

Homozygous recessive condition of citrullinemia is manifested by increasing ammonia and decreasing arginine concentrations in blood during the first 24 hours after birth. Affected calves display severe neurological dysfunction and death within 1 week as a result of a deficiency of the enzyme argininosuccinate synthetase. Problems of the central nervous system from the build-up of ammonia may include unsteady gait, aimless wandering, apparent blindness and head pressing. Prior to birth the dam is able to remove the excess ammonia.

Incidence of heterozygotes for citrullinemia has been estimated at less than .5% among U.S. Holsteins. Should we encourage elimination of this condition from the breed to avoid calf losses? Are there benefits to the carriers of this condition? The quick answers are yes and no respectively. Citrullinemia was not a useful indicator for economically important traits associated with milk, fat or protein. None of the traits representing biology were significantly different between cows normal or heterozygous for citrullinemia.

Bovine citrullinemia was not a useful marker for milk, fat and protein production because 1) the frequency of the defective allele was low and 2) within family differences were nonsignificant between normal and heterozygous half-sisters.

DUMPS

Deficiency of uridine monophosphate synthase (DUMPS) was unknown 20 years ago, a hot topic 10 years ago, aggressively tested for 5 years ago and forgotten now.

Testing of undesirable genetic conditions permits identification of carriers, their removal from the breeding population, deceased frequency of the condition and consequently reduced need for further testing. Elimination of BLAD, citrullinemia and DUMPS is not or has not had a significant impact on genetic progress for economically important traits.

TABLE 1.Frequency of BLAD by summary date

Frequency is among the top 400 AI active bulls in Jan. 1992

Frequency is among the new top 400 AI active bulls in July 1992 to Jan. 1995

TABLE 2. Frequency of BLAD among offspring of carrier sires

TABLE 3. Differences between carriers and normals for BLAD under the simple and complex analyses.

*P<.05

BLAD = Bovine Leukocyte Adhesion Deficiency

TPI = Type Production Index

PTA = Predicted Transmitting Ability