Farm management and husbandry practices associated with spontaneous humeral fractures in New Zealand dairy heifers

Figures & data

Figure 1. Causal diagram demonstrating the hypothesised relationships between the risk of humeral fracture and variables carried forward from a univariable analysis of farm and management factors associated with the risk of humeral fracture in dairy heifers. Dashed grey arrows show possible pathways for which there is less evidence.

Figure 2. Map of New Zealand showing the geographical location of farms that did (case; black squares) or did not (control; grey triangle) report cases of humeral fractures among dairy heifers. Four farms (two case and two control) are not shown due to farmers withholding their locations. Clusters of case farms are observed in the Waikato and Canterbury regions and clusters of control farms are observed in the Taranaki and lower South Island regions.

Table 1. Results of univariable logistic regression for association of farm characteristics and management factors with the unadjusted OR (95% CI) for risk of a farm having cases of spontaneous humeral fracture in dairy heifers.

Variable (global p-value)	Case farms (n = 35)	Control farms (n = 33)	OR (95% CI)	p-value^a
Breed (p < 0.001)
Holstein-Friesian	6/35 (17%)	17/33 (52%)	0.35 (0.13–0.85)	0.03
Jersey	1/35 (3%)	6/33 (18%)	0.47 (0.13–3.64)	0.52
Holstein-Friesian x Jersey	27/35 (77%)	10/33 (30%)	7.65 (2.47–26.72)	0.0007
Other^b	1/35 (3%)	0/33 (0%)	NA	NA
Calving pattern (p = 0.95)
Spring	33/35 (94%)	31/33 (94%)	1.06 (0.12–9.32)	0.95
Autumn	0/35 (0%)	0/33 (0%)	NA	NA
Split	2/35 (6%)	2/33 (6%)	1.00 (0.12–8.33)	1.00
Herd production 2018–2019 season (kg MS) (p = 0.15)
275–380	13/31 (42%)	5/29 (17%)	2.6 (0.98–8.1)	0.07
381–410	6/31 (19%)	7/29 (24%)	0.33 (0.07–1.44)	0.15
411–460	7/31 (23%)	7/29 (24%)	0.38 (0.08–1.64)	0.2
461–600	5/31 (16%)	10/29 (34%)	0.19 (0.04–0.81)	0.03
Frequency of milking (p = 0.57)
All once a day	2/35 (6%)	4/33 (12%)	0.36 (0.04–2.35)	0.49
All twice a day	22/35 (63%)	21/33 (64%)	0.76 (0.25–2.25)	0.62
Mix	11/35 (31%)	8/33 (24%)	1.38 (0.56–3.55)	0.49
Previous diagnosis of Cu deficiency (p = 0.25)	9/34 (26%)	5/33 (15%)	2.02 (0.61–7.32)	0.26
Supplement Cu (p = 0.31)	29/35 (83%)	24/33 (73%)	1.81 (0.57–6.1)	0.32
Supplement lime flour (p = 0.73)	23/35 (66%)	23/33 (70%)	0.83 (0.3–2.31)	0.73
Feed fodder beet (p = 0.19)	14/35 (40%)	10/33 (30%)	1.94 (0.72–5.38)	0.19
Growth check or health issues (p = 0.024)	8/28 (29%)	2/30 (7%)	5.6 (1.24–39.81)	0.041
Milk fed to calves (p = 0.26)
Whole milk	28/34 (82%)	20/31 (65%)	2.52 (0.75–9.28)	0.14
Milk powder	1/34 (3%)	2/31 (6%)	0.9 (0.04–11.95)	0.94
Both	5/34 (15%)	9/31 (29%)	0.56 (0.17–1.61)	0.29
Volume of milk fed (L/calf/day)^c (p = 0.89)	4.99 ± 1.33	4.9 ± 0.92	1.07 (0.7–1.65)	0.77
When meal fed to calves (p = 0.31)
Pre-weaning	3/35 (9%)	1/30 (3%)	2.63 (0.32–54.7)	0.41
Post-weaning	0/35 (0%)	1/30 (3%)	NA	NA
Both	32/35 (91%)	28/30 (93%)	1.14 (0.69–1.91)	0.61
Calf age when accessed pasture (weeks)^c (p = 0.022)	3.37 ± 1.91	4.53 ± 2.24	0.68 (0.47–0.90)	0.006

^a Significance of variable in univariable logistic model

^b Ayrshire

^c Mean ± SD

MS = milk solids; NA = not applicable

Figure 3. Graph showing the change in probability of humeral fracture among heifers for a farm where Holstein-Friesian Jersey crossbreed is the main breed of dairy cow (black line and dark 95% CI) or not (grey line and light grey 95% CI), over the range of ages that calves first had access to pasture.