Defence system

5.2.2.1. Genotype differences (red and black)

From 1999 till 2001 observations were made to study the genotype differences of defence system and ability (resistance), if exist, between the red and black coloured Holstein Friesian cows. At that time there was a change in the breeding goal at both stocks of C and D. To reach higher production, black sires were used instead of keeping red colour.

Table 27 presents that prevalence and detection of mastitis is much probable (45.3% and 100%) among black cows. It is because of the high production and therefore, lower resistance against environment. Red cows produce less milk but their power of resistance is higher. It is also worth to ponder over balancing the harmony of genotype and circumstances.

Table 27. Number of red and black cows sampled at stock C and D (12-13^th November, 1999)

Stock C Stock D

Group

n % n %

Σ cows 650 400

Productive 500 100 300 100

Σ red 447 89.4 295 98.3

Sampled 103 23.0 68 23.0

Σ black 53 10.6 5 1.6

Sampled 24 45.3 5 100

Σ sampled 127 25.4 73 24.3

The conformation of the cow significantly influences predisposition to mastitis reported Hámori (1974), Horváth (1982), Dohy (1985), Seykora and McDaniel (1985) etc. Because of the favourable relationship between some udder traits and SCC of milk, screening on udder characteristics may have slowed the genetic increase in susceptibility to mastitis (and so LSCS) (Rogers et al. 1991; Boettcher et al. 1998). Gulyás et al. (1998) and Gulyás and Iváncsics (1999) also reported the importance of udder morphology and the role of pigmented teat ends. Dohy (1985), Seykora and McDaniel (1986), Schutz et al. (1993) and Dohy (1999) suggested that sire analysts from AI organizations should screen perspective bull-dams for udder conformation traits and should eliminate cows with deep udders or wide front teats from consideration.

The structure of legs and hoofs is also important predisposing factor.

Movements involved getting feed and lying down are naturally necessary. Leg injuries in a herd are indicative of likely increase in udder diseases. However, long and untreated hoofs are often a question of mismanagement rather than a conformation fault of the cow (Markus, 1999 personal communication).

Culling cows with poor udder shape and leg injuries results in improved udder health.

5.2.2.2. Unusual correlations (“breakers”)

Schutz et al. (1990) suggested that mastitis as indicated by LSCS is more common during first lactations of cows with sires that transmit higher

milk yield, perhaps because of the stress from producing more milk. However, not all high-production bulls sire high rates of mastitis (Dunklee, 1991; Dohy 1999).

On the other hand, with the sire rankings for Predicted Transmitting Ability for Somatic Cell Score (PTASCS), producers can select bulls on their ability to sire daughters with lower rates of mastitis reported Emanuelson et al.

(1988), Banos and Shook (1990), Boettcher et al. (1992), Shook (1993) and Schutz et al. (1994). The sire evaluations will be reported in terms of a bull’s predicted transmitting ability for somatic cell score. If the difference of PTASCS of two bulls is 0.5 and daughters of these bulls are housed in the same herd at the same time, the SCS of the bull’s daughters is expected to differ by 0.5. Furthermore, the rankings of sires by PTASCS hold up across herds, regardless of mastitis-control levels in those herds. So, both high and low SCS herds can benefit from selection of the same sires with low PTASCS.

“Across herd” results

Figure 4, 5, 6 and 7 show overall means of milk production and somatic cell count of stock and progeny group of sire No. 9117 at farm A and B. Table 28 presents means of 305 days milk production, SCC and number of lactations at stock A, B and C. The number of lactations should always be taken into account!

Table 28. Means of 305 days milk production, SCC and number of lactations at stock A, B and C

Stock Group n Milk kg SCC x 1000 Lactation

mean 66 3998 *** 479 *** 3.3 NS

A 9117 23 4334 *** 737 *** 3.5 NS

mean 32 3027 *** 946 *** 3.7 *

B 9117 10 3433 *** 547 *** 4.1 *

mean 4614 6835 *** 328 ** 2.8 ***

C 9117 366 6025 *** 439 ** 4.8 ***

(level of significance: ***: p=0,1 %, **: p=1 %, *: p=5 %, +: p=10 %, NS=not significant)

“Within a herd” results

In stock C, 83 progeny groups of different sires were found by studying 4614 lactations. Based on pedigrees of sires closer relations can be noticed. Sire No. 12152 & 11762 and so 10748 & 9786 are in closer relations (Table 30-33).

Being extrapolated, all the selected progeny groups produced lower SCC of milk than calculated according to the number of lactation (5.2.1.3.). However, 305 days milk productions show larger differences (Table 29). Progeny groups of sire No. 12152 & 11762 produced more milk than the overall mean of the stock while progeny group of 9786 produced like mean and offsprings of sire No. 10749 produced less milk than the average. It reflects the importance of maternal ancestry. Sire analysts from AI organizations should screen perspective bull-dams for milk production and SCC and should eliminate cows with lower production and higher SCC during only a few lactation from consideration as suggested Dohy (1985), Seykora and McDaniel (1986), Schutz et al. (1993) and Dohy (1999).

Daughters of sire No. 9117 produced less milk but somatic cell count was less, too.

Table 29. Production traits, correlations and its significance of progeny groups of some sires at stock C

Table 30. Pedigree of sire 12152

S 5138

9212 CAN

- USA

12152 CAN

7668 4278

USA

USA

Table 31. Pedigree of sire 11762

S 5138

9212 CAN

- USA

11762 ^CAN

7668 4278

USA

USA

Table 32. Pedigree of sire 10748

HB 5138

9212 CAN

- USA

10748 ^CAN

5510 - CAN

USA USA

(D)

Table 33. Pedigree of sire 9786

HB 5138

9212 CAN

- USA

9786 CAN

5510 - CAN

USA USA

(D)

Genetic studies of dairy cattle have found that single-trait selection for higher milk production brings with it slightly higher rates of mastitis and other diseases. Therefore, selection only for those bulls with low PTASCS will be the same as selection for lower rates of improvement in milk yield (Boettcher et al., 1992; Da et al., 1992; Schutz et al., 1994).

Conclusions are as fallows:

• Environmental factors (keeping and milking hygiene, feeding etc.) may differ but genetic trends are “constant”. (However, because of the insufficient circumstances trends well known in the literature sometimes could not be seen.)

• The number of lactations should be known for correct evaluation of the udder health status of a cow/progeny group/stock.

• Younger cows (1^st lactation) usually produce less milk and less somatic cells in it.

• Cows in their 2^nd and 3^rd lactation produce a lot of milk but sometimes older cows (4^th lactation) are able to produce also higher yields than the overall mean of the stock. Remarkable that older cows, producing more milk, has lower somatic cell count in milk. It reflects the importance of the value of

“correlation breaker” sires and longevity of cows.

• The ESCC also allows a SCC (and SCS) calculation, which serves as a monitor of the udder health of a progeny group average in the herd.

• Studying the pedigrees of sires closer relations can be noticed that reflect the importance of maternal ancestry.

All in all, test day milk production and somatic cell count data are very important nowadays to ensure a reasonable production level and selection for mastitis resistance is necessary and could be efficient.

5.2.3. The use of a few screening methods

In document PhD THESIS (Pldal 80-85)