Nutritional Modification

Excellent reviews of nutritional strategies for managing heat-stressed dairy cows (West 1999), and poultry (Lin et al. 2006) have been published. Dietary manipulation has been shown to be beneficial for reducing the effects of heat stress in cattle (Beede and Collier 1986; Schneider et al. 1986; West et al. 1991; Mader et al. 1999b; Granzin and Gaughan 2002). A 'cold' dairy cow diet generates a high net nutrient proportion for milk production and lower heat increment (Gallardo 1998). The author indicates that some outstanding characteristics of 'cold' diets are: (1) higher energy contents per unit volume; (2) highly fermentable fiber; (3) lower protein degradability; and (4) high by-pass nutrients contents. These recommendations are useful when feeding totally mixed rations. However, diet manipulation may be useful even under grazing systems. Gallardo et al. (2001) found that hydrogenated fish fat could be a good ingredient to sustain high yields and elevated maintenance requirements in a grazing system during hot conditions. These are in reality, however, only short-term solutions. In many areas of the world, feeding grains and other high energy ingredients will not be financially sustainable. In many areas, animal production is based on grazing, foraging or browsing. A changing climate will impact on grasses, shrubs, and trees. If these effects are negative, then there will be significant changes in livestock production in the affected areas (see previous discussion).

Water is the most critical nutrient for animals. Climate change may have a number of impacts on water availability. In addition, water requirements are higher during periods of heat load (Winchester and Morris 1956; Beede and Collier 1986; Beatty et al. 2006). High production animals have a greater need for water compared to low production animals. Classical studies have demonstrated that water losses from animals increase with increasing air temperature (Kibler and Brody 1950; McDowell and Weldy 1960). Drinking behaviour is complex and is influenced by a number of factors such as diet, live weight, health status, and physiological status. Normally, it would be expected that water intake will increase when animals are exposed to hot conditions. Beatty et al. (2006) reported that water intake of Bos taurus heifers (331 kg) increased from approximately 19.8 L/head/day under cool conditions (wet bulb <25°C) to 31.4 L/head/day when exposed to a wet bulb temperature between 25°C and 33°C (Fig. 7.8). Water intakes reported by Gaughan and Tait (2005) for Angus steers (550 kg) exposed to hot conditions (36°C) were 41.1 L/head/day, up from 19.8 L/head/day under thermoneutral conditions (26°C). Concurrent feed intake fell from approximately 1.5% of body weight to almost zero (Beatty et al. 2006), and from approximately 2.4% of body weight to 1.8% of body weight (Gaughan and Tait 2005). For camels, feed intake was not affected when exposed to high heat load (40°C) provided they had access to water (Guerouali and Filali 1995). However, water intake increased by 300%. Other studies have shown that water intake decreases when feed intake is reduced (Chaiyabutr et al. 1980; Kadzere et al. 2002; Mader and Davis 2004). Goats (and other species) respond to water restrictions by reducing feed intake and concentrating their urine (Ahmed and

1 i ■_1 ■ ■_I_i_lJ_i_i_* 1 1 1 »■ ■ 1 j ■ 1 I_i_h_I_i_i_l_i_j_l_■ ■ I I ■ 1_i_i_L_i_i_I

□ ay of experimenl Day of experiment

1 i ■_1 ■ ■_I_i_lJ_i_i_* 1 1 1 »■ ■ 1 j ■ 1 I_i_h_I_i_i_l_i_j_l_■ ■ I I ■ 1_i_i_L_i_i_I

□ ay of experimenl Day of experiment

Fig. 7.8 Mean daily feed intake (a and b) and water intake (c and d) for Bos taurus and Bos indicus heifers. Points show the mean ± SEM for each of six animals. The horizontal bar under each figure indicates the hottest 5 days of the experiment. Asterisks under the data denote P < 0.05 for the day marked vs. the control days (days 1 and 2) (Beatty et al. 2006)

El Kheir, 2004). Offering warm rather than cool water has improved water intake of heat stressed animals in some cases (Lanham et al. 1986; Olsson and Hydbring 1996; Olsson et al. 1997). It is generally agreed that provision of good quality water is an important factor to manage nutrition during periods of high heat load.

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