**3. Contributing factors to animal stress**

## **3.1 On-farm factors**

#### *3.1.1 Use of growth promotors or hormone implant*

Metabolic modifiers enhance the animal body condition and health. Dikeman [7] referred those metabolic modifiers are those substances which improve animal growth rate, feed efficiency, dressing percentage, shelf life, palatability, nutritional composition and meat quality and they are given to animals in the form of feed, injection or implants. Almost every country except EU, use these modifiers in meat producing animals. Their effects on meat quality of ruminants especially on beef cattle can be studied in [7–10] reported that steroid implants could increase the dark cutting frequency of meat. Although, there is low dark cutting of meat by 35% average in heifers and 69% in steers if we implant the growth promotors to 100 or more days [9].

#### *3.1.2 Effect of animal gender*

Heifers are more prone to dark cutting than steers [11–13]. Estrogen makes "fighting" or guarded nature of the animal [11, 12] found that heifers show more excitable nature than steers. Kenny and Tarrant [14] reported that high pH meat is produced in result of mounting behavior during the estrous period. Therefore, it is suggested to prevent estrus in meat heifers and these comprise spaying, progestins administration and GnRH immunization [15, 16]. Scanga et al. [9] reported that spayed animals had low occurrence of dark cutting. Bass et al. [17] reported that heifers do not show

much difference in glycogen level due to acute and short type of physiological reaction, while the steers have chronic stress. So, during regrouping and other activities, glycogen depletion is increased with higher pHu and dark cutting.
