بسم الله الرحمن الرحيم
The animals are subject to their mother in lawfulness and unlawfulness. If the meat and milk of the mother is halal then the milk and meat of that animal shall also be halal.
وفى شرح الوهبانه للشرنبلالى عن جوامع الفقه والولو الجبية: الاعتبار فى المتولد للأم فى الأضحية والحل (شامى: 5/400)
The mother of a jersey cow is a cow whose meat and milk is halal; hence the milk and meat of jersey cow shall also be halal.
Allah knows Best!
Darul Uloom Deoband