Roles of maternal vision and olfaction in suckling-mediated inhibition of luteinizing hormone secretion, expression of maternal selectivity, and lactational performance of beef cows.
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The roles of maternal vision and olfaction in regulating the suckling-mediated inhibition of LH secretion, expression of maternal selectivity, and lactational performance was examined in anestrous beef cows (n = 57). Pluriparous cows were allotted randomly to one of 10 groups between 17 and 21 days postcalving (Experimental Day 0). Groups 1-8 included cows that were either intact, blind, anosmic, or blind and anosmic, and were control-suckled by either their own or unrelated ("alien") calves every 6 h for 6 days. Groups 9 and 10 served as positive controls and were left intact and weaned, or were anosmic, blind, and weaned. The frequency of LH pulses (pulses/5 h) remained unchanged over the 6-day experiment in sighted and olfactory-intact groups suckling their own calves (1.2 +/- 0.01). In contrast, cows that were olfactory-intact or sighted and suckling alien calves, blind and anosmic and suckling their own or alien calves, or weaned exhibited prompt increases (p < 0.001) in LH pulse frequency to a maximum of 4.6 +/- 0.3 pulses/5 h within 6 days. Mean frequency was greater in these groups (p < 0.05) than in olfactory-intact or sighted groups suckling their own calves. Enforced suckling by an alien calf attenuated (p < 0.001) milk production and calf weight gain, and a greater (p < 0.05) proportion of cows presented with aliens during behavioral tests physically rejected suckling compared to those presented with their own calves. These results confirm that suckling-related events sustain the inhibited pattern of LH secretion in cows only if the offspring are positively identified as their own. Olfaction and vision are equally effective in permitting calf identification, but elimination of both senses prevents calf identification and the negative effects of suckling on LH secretion.