(a) Justify why more than one digestibility trial needs to be conducted during indirect method of digestibility determination of…

(a) Why more than one trial is needed in the indirect method of digestibility

In the indirect (difference) method the test feed, such as a concentrate, cannot be fed alone, since it would upset rumen function. Digestibility of a basal roughage ration is found in one trial, and that of the basal ration plus the test feed in a second trial; the test feed's digestibility is calculated by difference. At least two trials are therefore inevitable, and the estimate depends on both.

More than one trial is also needed because: (1) the method assumes no associative effect between the basal and test feeds, so the trial is repeated at different levels of inclusion to check this; (2) individual animals differ in digestive capacity, so each trial uses several animals (at least 4–6) for reliable averages; (3) day-to-day variation in intake and faecal output demands a preliminary period of 10–14 days and collection of 7–10 days each; and (4) errors in the roughage trial carry into the difference calculation and get magnified, so replication improves accuracy.

(b) Physiological adjustments of goats in hot weather

Goats resist heat better than cattle, but adjust as follows. The main response is increased respiration rate and panting, which raises evaporative loss, with some sweating; pulse rate and rectal temperature rise a little. Peripheral vasodilation moves blood to the skin for radiation and convection, and blood volume may increase. Feed intake falls, especially of roughage, cutting the heat increment, while water intake rises, and desert breeds can conserve water by reducing urine and faecal water loss. Metabolic rate drops through lower thyroid hormone (T₃, T₄) secretion, and changes in aldosterone, antidiuretic hormone and cortisol help water and electrolyte balance. Animals seek shade, reduce activity and stand apart to lose heat. Prolonged stress reduces growth, milk yield and fertility.

(c) Stages of spermatogenesis in the bull

Spermatogenesis takes place in the seminiferous tubules and lasts about 61 days, nearly 4.5 cycles of the seminiferous epithelium of about 13.5 days each, with about 10 more days in epididymal transit. It has three phases:

1. Spermatocytogenesis: type A spermatogonia divide mitotically to renew the stem pool, then form intermediate and type B spermatogonia, which give primary spermatocytes.
2. Meiosis: primary spermatocytes undergo the first division to two secondary spermatocytes, and the second division to four haploid spermatids.
3. Spermiogenesis: spermatids transform, without division, into spermatozoa through Golgi, cap, acrosome and maturation phases, with nuclear condensation, flagellum formation and loss of excess cytoplasm.

Spermiation releases spermatozoa from Sertoli cells into the lumen. FSH, LH and testosterone regulate the process.

(d) Importance of goat rearing for the socio-economic upliftment of farmers

Goats are the "poor man's cow". They need little capital, land and housing, and suit landless, marginal and small farmers and women. They are hardy, adapt to harsh and arid areas, breed early and often (twins are common, about three kiddings in two years), and give quick returns. Chevon has steady demand with no religious taboo, and goat milk is easily digested and valued in nutrition; skin, hair and manure add income. Goats act as a living bank and insurance in drought and emergencies. Breeds such as Jamunapari, Barbari, Sirohi and Black Bengal support this. Goat rearing also provides women with income and work, and government support comes through the National Livestock Mission, including its entrepreneurship and breed improvement components.

(e) Covariance components for resemblance between relatives

Relatives resemble one another because they share genes and environment. For the variance components V_A (additive), V_D (dominance), V_I (epistasis) and V_Ec (common environment), the covariances (without inbreeding) are:

• Parent and offspring: ½V_A.
• Half sibs: ¼V_A.
• Full sibs: ½V_A + ¼V_D + V_Ec.
• Monozygotic twins: V_G, the total genetic variance (V_A + V_D + V_I).

Only additive variance is transmitted across generations, so resemblance between parents and offspring and between half sibs gives the heritability: h² = 2 × the parent–offspring regression and 4 × the half-sib intraclass correlation. Dominance shows only in full sibs and twins, and a common environment such as dam or litter raises the full-sib covariance, so half-sib analysis is preferred.