Determinants and improvements of calf parasite load, growth and behaviour on smallholder dairy farms in Kenya

This thesis research involving 187 heifer calves on 150 zero-grazing smallholder dairy farms in two Kenyan counties was designed with the following specific objectives: 1) to describe and determine animal- and farm-level factors associated with time-to-onset and fecal counts of strongyle-type eggs and coccidia oocysts (prospective cohort study); 2) to evaluate the effects of practical and affordable calf housing improvements on average daily gain (ADG) in weight during pre- and post-weaning periods (randomized controlled trial); 3) to determine the effect of environmental and comfort improvement on lying and sucking behaviours (randomized controlled trial); 4) to estimate the economic effects of implementing the low-cost housing enhancements and management changes in objectives 2-3 when raising a 15-month heifer (partial budget analysis). For objectives 2 and 3, intervention farms (n=75) received calf housing improvements that included: 1) filling of floor holes if on the ground or repairing wooden slats if on an elevated floor; 2) introduction of rubber mats on the lying area; 3) ensuring a floor gradient for drainage; 4) attaching a rubber nipple on the wall of the calf pen; and 5) patching leaking roofs, along with training on youngstock management. Up to six bimonthly farm visits were used to collect animal- and farm-level data, such as accelerometer readings for lying behaviours, heart girth for ADG of weight, and rectal fecal samples for McMaster floatation. For objective 1, Incidence risks of strongyle-type and coccidia over the study period were 28.3% (53/187) and 87.7% (164/187), respectively. For infected calves, median time-to-onset for strongyles and coccidia was 78 (interquartile-range: IQR 38-117) and 43 (IQR 29-92) days, respectively. In the final Cox proportional hazard (PH) model for strongyles, breed (Ayrshires and Jerseys) and weaned calves had a greater hazard of infection than Friesians and preweaned calves, respectively. Calf tethering outside the pen sometimes was associated with a higher hazard of strongyle infection. In the final Cox PH model for coccidia, calves with watery and/or hemorrhagic diarrhea had a higher hazard compared with those with hard or soft feces. Weaning status and birth weight (kg) were time-varying covariates, leading to increased hazard over time. In the final mixed-effects negative binomial (MeNB) model for strongyles, weaned animals had higher counts than those still on milk. In an interaction variable, the predicted strongyletype egg counts increased with longer duration of farm operation when herd size was less than five cattle but decreased when herd size was more than five. In the final MeNB model for coccidia, calves sometimes tethered outside their pens had higher counts than those continuously enclosed in the pen. Calf pen floors with either scant manure or moderate slurry had higher predicted counts than those on a clean pen floor. Calves with watery or hemorrhagic diarrhea and fed fresh Napier grass (Pennisetum purpureum) had higher counts compared with soft or hard feces and those not given fresh Napier, respectively. In an interaction variable, calves experiencing diarrhea and raised on elevated slatted floors had lower oocyst counts compared with those having diarrhea but not on elevated floors. In conclusion, the identified management practices associated with onset and counts of gastrointestinal parasitism should be considered in control efforts. For objective 2, Median pre-weaning and post-weaning ADGs were 0.307 and 0.487 kg/d, respectively. In the final pre-weaning model (p<0.050), factors positively associated with ln ADG were calf age at first acaricide application, and total number of calf pens, while factors negatively associated with ln ADG included calf mortality risk over the last five years and calf age at first free access to water. In an interaction term, for calves from parity 3+ dams, ADG was lower when milk was fed twice/day than thrice/day, with no difference in calves of lower parity dams. In a second interaction term, ADG was similar by principal farmer gender at higher levels of education, but significantly lower for female than male principal farmers when only primary education was achieved. In the final post-weaning model, housing improvements increased ADG by 5.6%. Other factors positively associated with post-weaning ADG were feeding of calf pellets, wheat bran, maize bran, and hay. Calf age at first introduction of concentrate, calf mortality risk over the last five years, and principal farmer age were negatively associated with ADG. In an interaction term, ADG was high when there were fecal coccidia oocysts and when calves had visual or physical contact with their dams, but low when fecal coccidia cysts were present, and these dam-calf connections were absent. In a second interaction term, ADG increased with more calf pens for female principal farmers, while remaining low for male principal farmers. In conclusion, while controlling for other factors of ADG, making affordable calf housing improvements enhanced ADG, particularly during the postweaning period. For objective 3, The daily lying times and lying bout durations, over the visits, averaged 12.6-16.9 hr/d and 67.9-86.7 min/bout, respectively, while the median for the frequency of lying bouts was between 30-46/day. Provision of rubber nipples for nonnutritive sucking lowered proportions of cross-sucking, self-sucking and object-sucking behaviours slightly but not significantly. In the final mixed-effects linear regression model on daily lying time, superficial lymph node enlargement, body condition score and use of wood shaving/sawdust/crop waste as beddings had positive associations. In contrast, group housing and rubber mat use had negative associations. In an interaction term, lying time was significantly higher for calves on clean versus dirty floors if the age was